summaryrefslogtreecommitdiffstats
path: root/mm/vmscan.c
blob: 15b483ef6440d3a45ba69816159f7bf7ecc9915b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/mm/vmscan.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Swap reorganised 29.12.95, Stephen Tweedie.
 *  kswapd added: 7.1.96  sct
 *  Removed kswapd_ctl limits, and swap out as many pages as needed
 *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
 *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
 *  Multiqueue VM started 5.8.00, Rik van Riel.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/mm.h>
#include <linux/sched/mm.h>
#include <linux/module.h>
#include <linux/gfp.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/highmem.h>
#include <linux/vmpressure.h>
#include <linux/vmstat.h>
#include <linux/file.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h>	/* for try_to_release_page(),
					buffer_heads_over_limit */
#include <linux/mm_inline.h>
#include <linux/backing-dev.h>
#include <linux/rmap.h>
#include <linux/topology.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/compaction.h>
#include <linux/notifier.h>
#include <linux/rwsem.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/memcontrol.h>
#include <linux/delayacct.h>
#include <linux/sysctl.h>
#include <linux/oom.h>
#include <linux/prefetch.h>
#include <linux/printk.h>
#include <linux/dax.h>

#include <asm/tlbflush.h>
#include <asm/div64.h>

#include <linux/swapops.h>
#include <linux/balloon_compaction.h>

#include "internal.h"

#define CREATE_TRACE_POINTS
#include <trace/events/vmscan.h>

struct scan_control {
	/* How many pages shrink_list() should reclaim */
	unsigned long nr_to_reclaim;

	/* This context's GFP mask */
	gfp_t gfp_mask;

	/* Allocation order */
	int order;

	/*
	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
	 * are scanned.
	 */
	nodemask_t	*nodemask;

	/*
	 * The memory cgroup that hit its limit and as a result is the
	 * primary target of this reclaim invocation.
	 */
	struct mem_cgroup *target_mem_cgroup;

	/* Scan (total_size >> priority) pages at once */
	int priority;

	/* The highest zone to isolate pages for reclaim from */
	enum zone_type reclaim_idx;

	/* Writepage batching in laptop mode; RECLAIM_WRITE */
	unsigned int may_writepage:1;

	/* Can mapped pages be reclaimed? */
	unsigned int may_unmap:1;

	/* Can pages be swapped as part of reclaim? */
	unsigned int may_swap:1;

	/*
	 * Cgroups are not reclaimed below their configured memory.low,
	 * unless we threaten to OOM. If any cgroups are skipped due to
	 * memory.low and nothing was reclaimed, go back for memory.low.
	 */
	unsigned int memcg_low_reclaim:1;
	unsigned int memcg_low_skipped:1;

	unsigned int hibernation_mode:1;

	/* One of the zones is ready for compaction */
	unsigned int compaction_ready:1;

	/* Incremented by the number of inactive pages that were scanned */
	unsigned long nr_scanned;

	/* Number of pages freed so far during a call to shrink_zones() */
	unsigned long nr_reclaimed;
};

#ifdef ARCH_HAS_PREFETCH
#define prefetch_prev_lru_page(_page, _base, _field)			\
	do {								\
		if ((_page)->lru.prev != _base) {			\
			struct page *prev;				\
									\
			prev = lru_to_page(&(_page->lru));		\
			prefetch(&prev->_field);			\
		}							\
	} while (0)
#else
#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
#endif

#ifdef ARCH_HAS_PREFETCHW
#define prefetchw_prev_lru_page(_page, _base, _field)			\
	do {								\
		if ((_page)->lru.prev != _base) {			\
			struct page *prev;				\
									\
			prev = lru_to_page(&(_page->lru));		\
			prefetchw(&prev->_field);			\
		}							\
	} while (0)
#else
#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
#endif

/*
 * From 0 .. 100.  Higher means more swappy.
 */
int vm_swappiness = 60;
/*
 * The total number of pages which are beyond the high watermark within all
 * zones.
 */
unsigned long vm_total_pages;

static LIST_HEAD(shrinker_list);
static DECLARE_RWSEM(shrinker_rwsem);

#ifdef CONFIG_MEMCG
static bool global_reclaim(struct scan_control *sc)
{
	return !sc->target_mem_cgroup;
}

/**
 * sane_reclaim - is the usual dirty throttling mechanism operational?
 * @sc: scan_control in question
 *
 * The normal page dirty throttling mechanism in balance_dirty_pages() is
 * completely broken with the legacy memcg and direct stalling in
 * shrink_page_list() is used for throttling instead, which lacks all the
 * niceties such as fairness, adaptive pausing, bandwidth proportional
 * allocation and configurability.
 *
 * This function tests whether the vmscan currently in progress can assume
 * that the normal dirty throttling mechanism is operational.
 */
static bool sane_reclaim(struct scan_control *sc)
{
	struct mem_cgroup *memcg = sc->target_mem_cgroup;

	if (!memcg)
		return true;
#ifdef CONFIG_CGROUP_WRITEBACK
	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
		return true;
#endif
	return false;
}
#else
static bool global_reclaim(struct scan_control *sc)
{
	return true;
}

static bool sane_reclaim(struct scan_control *sc)
{
	return true;
}
#endif

/*
 * This misses isolated pages which are not accounted for to save counters.
 * As the data only determines if reclaim or compaction continues, it is
 * not expected that isolated pages will be a dominating factor.
 */
unsigned long zone_reclaimable_pages(struct zone *zone)
{
	unsigned long nr;

	nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
		zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
	if (get_nr_swap_pages() > 0)
		nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
			zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);

	return nr;
}

unsigned long pgdat_reclaimable_pages(struct pglist_data *pgdat)
{
	unsigned long nr;

	nr = node_page_state_snapshot(pgdat, NR_ACTIVE_FILE) +
	     node_page_state_snapshot(pgdat, NR_INACTIVE_FILE) +
	     node_page_state_snapshot(pgdat, NR_ISOLATED_FILE);

	if (get_nr_swap_pages() > 0)
		nr += node_page_state_snapshot(pgdat, NR_ACTIVE_ANON) +
		      node_page_state_snapshot(pgdat, NR_INACTIVE_ANON) +
		      node_page_state_snapshot(pgdat, NR_ISOLATED_ANON);

	return nr;
}

/**
 * lruvec_lru_size -  Returns the number of pages on the given LRU list.
 * @lruvec: lru vector
 * @lru: lru to use
 * @zone_idx: zones to consider (use MAX_NR_ZONES for the whole LRU list)
 */
unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone_idx)
{
	unsigned long lru_size;
	int zid;

	if (!mem_cgroup_disabled())
		lru_size = mem_cgroup_get_lru_size(lruvec, lru);
	else
		lru_size = node_page_state(lruvec_pgdat(lruvec), NR_LRU_BASE + lru);

	for (zid = zone_idx + 1; zid < MAX_NR_ZONES; zid++) {
		struct zone *zone = &lruvec_pgdat(lruvec)->node_zones[zid];
		unsigned long size;

		if (!managed_zone(zone))
			continue;

		if (!mem_cgroup_disabled())
			size = mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
		else
			size = zone_page_state(&lruvec_pgdat(lruvec)->node_zones[zid],
				       NR_ZONE_LRU_BASE + lru);
		lru_size -= min(size, lru_size);
	}

	return lru_size;

}

/*
 * Add a shrinker callback to be called from the vm.
 */
int register_shrinker(struct shrinker *shrinker)
{
	size_t size = sizeof(*shrinker->nr_deferred);

	if (shrinker->flags & SHRINKER_NUMA_AWARE)
		size *= nr_node_ids;

	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
	if (!shrinker->nr_deferred)
		return -ENOMEM;

	down_write(&shrinker_rwsem);
	list_add_tail(&shrinker->list, &shrinker_list);
	up_write(&shrinker_rwsem);
	return 0;
}
EXPORT_SYMBOL(register_shrinker);

/*
 * Remove one
 */
void unregister_shrinker(struct shrinker *shrinker)
{
	down_write(&shrinker_rwsem);
	list_del(&shrinker->list);
	up_write(&shrinker_rwsem);
	kfree(shrinker->nr_deferred);
}
EXPORT_SYMBOL(unregister_shrinker);

#define SHRINK_BATCH 128

static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
				    struct shrinker *shrinker,
				    unsigned long nr_scanned,
				    unsigned long nr_eligible)
{
	unsigned long freed = 0;
	unsigned long long delta;
	long total_scan;
	long freeable;
	long nr;
	long new_nr;
	int nid = shrinkctl->nid;
	long batch_size = shrinker->batch ? shrinker->batch
					  : SHRINK_BATCH;
	long scanned = 0, next_deferred;

	freeable = shrinker->count_objects(shrinker, shrinkctl);
	if (freeable == 0)
		return 0;

	/*
	 * copy the current shrinker scan count into a local variable
	 * and zero it so that other concurrent shrinker invocations
	 * don't also do this scanning work.
	 */
	nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);

	total_scan = nr;
	delta = (4 * nr_scanned) / shrinker->seeks;
	delta *= freeable;
	do_div(delta, nr_eligible + 1);
	total_scan += delta;
	if (total_scan < 0) {
		pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
		       shrinker->scan_objects, total_scan);
		total_scan = freeable;
		next_deferred = nr;
	} else
		next_deferred = total_scan;

	/*
	 * We need to avoid excessive windup on filesystem shrinkers
	 * due to large numbers of GFP_NOFS allocations causing the
	 * shrinkers to return -1 all the time. This results in a large
	 * nr being built up so when a shrink that can do some work
	 * comes along it empties the entire cache due to nr >>>
	 * freeable. This is bad for sustaining a working set in
	 * memory.
	 *
	 * Hence only allow the shrinker to scan the entire cache when
	 * a large delta change is calculated directly.
	 */
	if (delta < freeable / 4)
		total_scan = min(total_scan, freeable / 2);

	/*
	 * Avoid risking looping forever due to too large nr value:
	 * never try to free more than twice the estimate number of
	 * freeable entries.
	 */
	if (total_scan > freeable * 2)
		total_scan = freeable * 2;

	trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
				   nr_scanned, nr_eligible,
				   freeable, delta, total_scan);

	/*
	 * Normally, we should not scan less than batch_size objects in one
	 * pass to avoid too frequent shrinker calls, but if the slab has less
	 * than batch_size objects in total and we are really tight on memory,
	 * we will try to reclaim all available objects, otherwise we can end
	 * up failing allocations although there are plenty of reclaimable
	 * objects spread over several slabs with usage less than the
	 * batch_size.
	 *
	 * We detect the "tight on memory" situations by looking at the total
	 * number of objects we want to scan (total_scan). If it is greater
	 * than the total number of objects on slab (freeable), we must be
	 * scanning at high prio and therefore should try to reclaim as much as
	 * possible.
	 */
	while (total_scan >= batch_size ||
	       total_scan >= freeable) {
		unsigned long ret;
		unsigned long nr_to_scan = min(batch_size, total_scan);

		shrinkctl->nr_to_scan = nr_to_scan;
		shrinkctl->nr_scanned = nr_to_scan;
		ret = shrinker->scan_objects(shrinker, shrinkctl);
		if (ret == SHRINK_STOP)
			break;
		freed += ret;

		count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
		total_scan -= shrinkctl->nr_scanned;
		scanned += shrinkctl->nr_scanned;

		cond_resched();
	}

	if (next_deferred >= scanned)
		next_deferred -= scanned;
	else
		next_deferred = 0;
	/*
	 * move the unused scan count back into the shrinker in a
	 * manner that handles concurrent updates. If we exhausted the
	 * scan, there is no need to do an update.
	 */
	if (next_deferred > 0)
		new_nr = atomic_long_add_return(next_deferred,
						&shrinker->nr_deferred[nid]);
	else
		new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);

	trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
	return freed;
}

/**
 * shrink_slab - shrink slab caches
 * @gfp_mask: allocation context
 * @nid: node whose slab caches to target
 * @memcg: memory cgroup whose slab caches to target
 * @nr_scanned: pressure numerator
 * @nr_eligible: pressure denominator
 *
 * Call the shrink functions to age shrinkable caches.
 *
 * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
 * unaware shrinkers will receive a node id of 0 instead.
 *
 * @memcg specifies the memory cgroup to target. If it is not NULL,
 * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
 * objects from the memory cgroup specified. Otherwise, only unaware
 * shrinkers are called.
 *
 * @nr_scanned and @nr_eligible form a ratio that indicate how much of
 * the available objects should be scanned.  Page reclaim for example
 * passes the number of pages scanned and the number of pages on the
 * LRU lists that it considered on @nid, plus a bias in @nr_scanned
 * when it encountered mapped pages.  The ratio is further biased by
 * the ->seeks setting of the shrink function, which indicates the
 * cost to recreate an object relative to that of an LRU page.
 *
 * Returns the number of reclaimed slab objects.
 */
static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
				 struct mem_cgroup *memcg,
				 unsigned long nr_scanned,
				 unsigned long nr_eligible)
{
	struct shrinker *shrinker;
	unsigned long freed = 0;

	if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)))
		return 0;

	if (nr_scanned == 0)
		nr_scanned = SWAP_CLUSTER_MAX;

	if (!down_read_trylock(&shrinker_rwsem)) {
		/*
		 * If we would return 0, our callers would understand that we
		 * have nothing else to shrink and give up trying. By returning
		 * 1 we keep it going and assume we'll be able to shrink next
		 * time.
		 */
		freed = 1;
		goto out;
	}

	list_for_each_entry(shrinker, &shrinker_list, list) {
		struct shrink_control sc = {
			.gfp_mask = gfp_mask,
			.nid = nid,
			.memcg = memcg,
		};

		/*
		 * If kernel memory accounting is disabled, we ignore
		 * SHRINKER_MEMCG_AWARE flag and call all shrinkers
		 * passing NULL for memcg.
		 */
		if (memcg_kmem_enabled() &&
		    !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
			continue;

		if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
			sc.nid = 0;

		freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible);
	}

	up_read(&shrinker_rwsem);
out:
	cond_resched();
	return freed;
}

void drop_slab_node(int nid)
{
	unsigned long freed;

	do {
		struct mem_cgroup *memcg = NULL;

		freed = 0;
		do {
			freed += shrink_slab(GFP_KERNEL, nid, memcg,
					     1000, 1000);
		} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
	} while (freed > 10);
}

void drop_slab(void)
{
	int nid;

	for_each_online_node(nid)
		drop_slab_node(nid);
}

static inline int is_page_cache_freeable(struct page *page)
{
	/*
	 * A freeable page cache page is referenced only by the caller
	 * that isolated the page, the page cache radix tree and
	 * optional buffer heads at page->private.
	 */
	int radix_pins = PageTransHuge(page) && PageSwapCache(page) ?
		HPAGE_PMD_NR : 1;
	return page_count(page) - page_has_private(page) == 1 + radix_pins;
}

static int may_write_to_inode(struct inode *inode, struct scan_control *sc)
{
	if (current->flags & PF_SWAPWRITE)
		return 1;
	if (!inode_write_congested(inode))
		return 1;
	if (inode_to_bdi(inode) == current->backing_dev_info)
		return 1;
	return 0;
}

/*
 * We detected a synchronous write error writing a page out.  Probably
 * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 * fsync(), msync() or close().
 *
 * The tricky part is that after writepage we cannot touch the mapping: nothing
 * prevents it from being freed up.  But we have a ref on the page and once
 * that page is locked, the mapping is pinned.
 *
 * We're allowed to run sleeping lock_page() here because we know the caller has
 * __GFP_FS.
 */
static void handle_write_error(struct address_space *mapping,
				struct page *page, int error)
{
	lock_page(page);
	if (page_mapping(page) == mapping)
		mapping_set_error(mapping, error);
	unlock_page(page);
}

/* possible outcome of pageout() */
typedef enum {
	/* failed to write page out, page is locked */
	PAGE_KEEP,
	/* move page to the active list, page is locked */
	PAGE_ACTIVATE,
	/* page has been sent to the disk successfully, page is unlocked */
	PAGE_SUCCESS,
	/* page is clean and locked */
	PAGE_CLEAN,
} pageout_t;

/*
 * pageout is called by shrink_page_list() for each dirty page.
 * Calls ->writepage().
 */
static pageout_t pageout(struct page *page, struct address_space *mapping,
			 struct scan_control *sc)
{
	/*
	 * If the page is dirty, only perform writeback if that write
	 * will be non-blocking.  To prevent this allocation from being
	 * stalled by pagecache activity.  But note that there may be
	 * stalls if we need to run get_block().  We could test
	 * PagePrivate for that.
	 *
	 * If this process is currently in __generic_file_write_iter() against
	 * this page's queue, we can perform writeback even if that
	 * will block.
	 *
	 * If the page is swapcache, write it back even if that would
	 * block, for some throttling. This happens by accident, because
	 * swap_backing_dev_info is bust: it doesn't reflect the
	 * congestion state of the swapdevs.  Easy to fix, if needed.
	 */
	if (!is_page_cache_freeable(page))
		return PAGE_KEEP;
	if (!mapping) {
		/*
		 * Some data journaling orphaned pages can have
		 * page->mapping == NULL while being dirty with clean buffers.
		 */
		if (page_has_private(page)) {
			if (try_to_free_buffers(page)) {
				ClearPageDirty(page);
				pr_info("%s: orphaned page\n", __func__);
				return PAGE_CLEAN;
			}
		}
		return PAGE_KEEP;
	}
	if (mapping->a_ops->writepage == NULL)
		return PAGE_ACTIVATE;
	if (!may_write_to_inode(mapping->host, sc))
		return PAGE_KEEP;

	if (clear_page_dirty_for_io(page)) {
		int res;
		struct writeback_control wbc = {
			.sync_mode = WB_SYNC_NONE,
			.nr_to_write = SWAP_CLUSTER_MAX,
			.range_start = 0,
			.range_end = LLONG_MAX,
			.for_reclaim = 1,
		};

		SetPageReclaim(page);
		res = mapping->a_ops->writepage(page, &wbc);
		if (res < 0)
			handle_write_error(mapping, page, res);
		if (res == AOP_WRITEPAGE_ACTIVATE) {
			ClearPageReclaim(page);
			return PAGE_ACTIVATE;
		}

		if (!PageWriteback(page)) {
			/* synchronous write or broken a_ops? */
			ClearPageReclaim(page);
		}
		trace_mm_vmscan_writepage(page);
		inc_node_page_state(page, NR_VMSCAN_WRITE);
		return PAGE_SUCCESS;
	}

	return PAGE_CLEAN;
}

/*
 * Same as remove_mapping, but if the page is removed from the mapping, it
 * gets returned with a refcount of 0.
 */
static int __remove_mapping(struct address_space *mapping, struct page *page,
			    bool reclaimed)
{
	unsigned long flags;
	int refcount;

	BUG_ON(!PageLocked(page));
	BUG_ON(mapping != page_mapping(page));

	spin_lock_irqsave(&mapping->tree_lock, flags);
	/*
	 * The non racy check for a busy page.
	 *
	 * Must be careful with the order of the tests. When someone has
	 * a ref to the page, it may be possible that they dirty it then
	 * drop the reference. So if PageDirty is tested before page_count
	 * here, then the following race may occur:
	 *
	 * get_user_pages(&page);
	 * [user mapping goes away]
	 * write_to(page);
	 *				!PageDirty(page)    [good]
	 * SetPageDirty(page);
	 * put_page(page);
	 *				!page_count(page)   [good, discard it]
	 *
	 * [oops, our write_to data is lost]
	 *
	 * Reversing the order of the tests ensures such a situation cannot
	 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
	 * load is not satisfied before that of page->_refcount.
	 *
	 * Note that if SetPageDirty is always performed via set_page_dirty,
	 * and thus under tree_lock, then this ordering is not required.
	 */
	if (unlikely(PageTransHuge(page)) && PageSwapCache(page))
		refcount = 1 + HPAGE_PMD_NR;
	else
		refcount = 2;
	if (!page_ref_freeze(page, refcount))
		goto cannot_free;
	/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
	if (unlikely(PageDirty(page))) {
		page_ref_unfreeze(page, refcount);
		goto cannot_free;
	}

	if (PageSwapCache(page)) {
		swp_entry_t swap = { .val = page_private(page) };
		mem_cgroup_swapout(page, swap);
		__delete_from_swap_cache(page);
		spin_unlock_irqrestore(&mapping->tree_lock, flags);
		put_swap_page(page, swap);
	} else {
		void (*freepage)(struct page *);
		void *shadow = NULL;

		freepage = mapping->a_ops->freepage;
		/*
		 * Remember a shadow entry for reclaimed file cache in
		 * order to detect refaults, thus thrashing, later on.
		 *
		 * But don't store shadows in an address space that is
		 * already exiting.  This is not just an optizimation,
		 * inode reclaim needs to empty out the radix tree or
		 * the nodes are lost.  Don't plant shadows behind its
		 * back.
		 *
		 * We also don't store shadows for DAX mappings because the
		 * only page cache pages found in these are zero pages
		 * covering holes, and because we don't want to mix DAX
		 * exceptional entries and shadow exceptional entries in the
		 * same page_tree.
		 */
		if (reclaimed && page_is_file_cache(page) &&
		    !mapping_exiting(mapping) && !dax_mapping(mapping))
			shadow = workingset_eviction(mapping, page);
		__delete_from_page_cache(page, shadow);
		spin_unlock_irqrestore(&mapping->tree_lock, flags);

		if (freepage != NULL)
			freepage(page);
	}

	return 1;

cannot_free:
	spin_unlock_irqrestore(&mapping->tree_lock, flags);
	return 0;
}

/*
 * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
 * someone else has a ref on the page, abort and return 0.  If it was
 * successfully detached, return 1.  Assumes the caller has a single ref on
 * this page.
 */
int remove_mapping(struct address_space *mapping, struct page *page)
{
	if (__remove_mapping(mapping, page, false)) {
		/*
		 * Unfreezing the refcount with 1 rather than 2 effectively
		 * drops the pagecache ref for us without requiring another
		 * atomic operation.
		 */
		page_ref_unfreeze(page, 1);
		return 1;
	}
	return 0;
}

/**
 * putback_lru_page - put previously isolated page onto appropriate LRU list
 * @page: page to be put back to appropriate lru list
 *
 * Add previously isolated @page to appropriate LRU list.
 * Page may still be unevictable for other reasons.
 *
 * lru_lock must not be held, interrupts must be enabled.
 */
void putback_lru_page(struct page *page)
{
	bool is_unevictable;
	int was_unevictable = PageUnevictable(page);

	VM_BUG_ON_PAGE(PageLRU(page), page);

redo:
	ClearPageUnevictable(page);

	if (page_evictable(page)) {
		/*
		 * For evictable pages, we can use the cache.
		 * In event of a race, worst case is we end up with an
		 * unevictable page on [in]active list.
		 * We know how to handle that.
		 */
		is_unevictable = false;
		lru_cache_add(page);
	} else {
		/*
		 * Put unevictable pages directly on zone's unevictable
		 * list.
		 */
		is_unevictable = true;
		add_page_to_unevictable_list(page);
		/*
		 * When racing with an mlock or AS_UNEVICTABLE clearing
		 * (page is unlocked) make sure that if the other thread
		 * does not observe our setting of PG_lru and fails
		 * isolation/check_move_unevictable_pages,
		 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
		 * the page back to the evictable list.
		 *
		 * The other side is TestClearPageMlocked() or shmem_lock().
		 */
		smp_mb();
	}

	/*
	 * page's status can change while we move it among lru. If an evictable
	 * page is on unevictable list, it never be freed. To avoid that,
	 * check after we added it to the list, again.
	 */
	if (is_unevictable && page_evictable(page)) {
		if (!isolate_lru_page(page)) {
			put_page(page);
			goto redo;
		}
		/* This means someone else dropped this page from LRU
		 * So, it will be freed or putback to LRU again. There is
		 * nothing to do here.
		 */
	}

	if (was_unevictable && !is_unevictable)
		count_vm_event(UNEVICTABLE_PGRESCUED);
	else if (!was_unevictable && is_unevictable)
		count_vm_event(UNEVICTABLE_PGCULLED);

	put_page(page);		/* drop ref from isolate */
}

enum page_references {
	PAGEREF_RECLAIM,
	PAGEREF_RECLAIM_CLEAN,
	PAGEREF_KEEP,
	PAGEREF_ACTIVATE,
};

static enum page_references page_check_references(struct page *page,
						  struct scan_control *sc)
{
	int referenced_ptes, referenced_page;
	unsigned long vm_flags;

	referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
					  &vm_flags);
	referenced_page = TestClearPageReferenced(page);

	/*
	 * Mlock lost the isolation race with us.  Let try_to_unmap()
	 * move the page to the unevictable list.
	 */
	if (vm_flags & VM_LOCKED)
		return PAGEREF_RECLAIM;

	if (referenced_ptes) {
		if (PageSwapBacked(page))
			return PAGEREF_ACTIVATE;
		/*
		 * All mapped pages start out with page table
		 * references from the instantiating fault, so we need
		 * to look twice if a mapped file page is used more
		 * than once.
		 *
		 * Mark it and spare it for another trip around the
		 * inactive list.  Another page table reference will
		 * lead to its activation.
		 *
		 * Note: the mark is set for activated pages as well
		 * so that recently deactivated but used pages are
		 * quickly recovered.
		 */
		SetPageReferenced(page);

		if (referenced_page || referenced_ptes > 1)
			return PAGEREF_ACTIVATE;

		/*
		 * Activate file-backed executable pages after first usage.
		 */
		if (vm_flags & VM_EXEC)
			return PAGEREF_ACTIVATE;

		return PAGEREF_KEEP;
	}

	/* Reclaim if clean, defer dirty pages to writeback */
	if (referenced_page && !PageSwapBacked(page))
		return PAGEREF_RECLAIM_CLEAN;

	return PAGEREF_RECLAIM;
}

/* Check if a page is dirty or under writeback */
static void page_check_dirty_writeback(struct page *page,
				       bool *dirty, bool *writeback)
{
	struct address_space *mapping;

	/*
	 * Anonymous pages are not handled by flushers and must be written
	 * from reclaim context. Do not stall reclaim based on them
	 */
	if (!page_is_file_cache(page) ||
	    (PageAnon(page) && !PageSwapBacked(page))) {
		*dirty = false;
		*writeback = false;
		return;
	}

	/* By default assume that the page flags are accurate */
	*dirty = PageDirty(page);
	*writeback = PageWriteback(page);

	/* Verify dirty/writeback state if the filesystem supports it */
	if (!page_has_private(page))
		return;

	mapping = page_mapping(page);
	if (mapping && mapping->a_ops->is_dirty_writeback)
		mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
}

struct reclaim_stat {
	unsigned nr_dirty;
	unsigned nr_unqueued_dirty;
	unsigned nr_congested;
	unsigned nr_writeback;
	unsigned nr_immediate;
	unsigned nr_activate;
	unsigned nr_ref_keep;
	unsigned nr_unmap_fail;
};

/*
 * shrink_page_list() returns the number of reclaimed pages
 */
static unsigned long shrink_page_list(struct list_head *page_list,
				      struct pglist_data *pgdat,
				      struct scan_control *sc,
				      enum ttu_flags ttu_flags,
				      struct reclaim_stat *stat,
				      bool force_reclaim)
{
	LIST_HEAD(ret_pages);
	LIST_HEAD(free_pages);
	int pgactivate = 0;
	unsigned nr_unqueued_dirty = 0;
	unsigned nr_dirty = 0;
	unsigned nr_congested = 0;
	unsigned nr_reclaimed = 0;
	unsigned nr_writeback = 0;
	unsigned nr_immediate = 0;
	unsigned nr_ref_keep = 0;
	unsigned nr_unmap_fail = 0;

	cond_resched();

	while (!list_empty(page_list)) {
		struct address_space *mapping;
		struct page *page;
		int may_enter_fs;
		enum page_references references = PAGEREF_RECLAIM_CLEAN;
		bool dirty, writeback;

		cond_resched();

		page = lru_to_page(page_list);
		list_del(&page->lru);

		if (!trylock_page(page))
			goto keep;

		VM_BUG_ON_PAGE(PageActive(page), page);

		sc->nr_scanned++;

		if (unlikely(!page_evictable(page)))
			goto activate_locked;

		if (!sc->may_unmap && page_mapped(page))
			goto keep_locked;

		/* Double the slab pressure for mapped and swapcache pages */
		if ((page_mapped(page) || PageSwapCache(page)) &&
		    !(PageAnon(page) && !PageSwapBacked(page)))
			sc->nr_scanned++;

		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));

		/*
		 * The number of dirty pages determines if a zone is marked
		 * reclaim_congested which affects wait_iff_congested. kswapd
		 * will stall and start writing pages if the tail of the LRU
		 * is all dirty unqueued pages.
		 */
		page_check_dirty_writeback(page, &dirty, &writeback);
		if (dirty || writeback)
			nr_dirty++;

		if (dirty && !writeback)
			nr_unqueued_dirty++;

		/*
		 * Treat this page as congested if the underlying BDI is or if
		 * pages are cycling through the LRU so quickly that the
		 * pages marked for immediate reclaim are making it to the
		 * end of the LRU a second time.
		 */
		mapping = page_mapping(page);
		if (((dirty || writeback) && mapping &&
		     inode_write_congested(mapping->host)) ||
		    (writeback && PageReclaim(page)))
			nr_congested++;

		/*
		 * If a page at the tail of the LRU is under writeback, there
		 * are three cases to consider.
		 *
		 * 1) If reclaim is encountering an excessive number of pages
		 *    under writeback and this page is both under writeback and
		 *    PageReclaim then it indicates that pages are being queued
		 *    for IO but are being recycled through the LRU before the
		 *    IO can complete. Waiting on the page itself risks an
		 *    indefinite stall if it is impossible to writeback the
		 *    page due to IO error or disconnected storage so instead
		 *    note that the LRU is being scanned too quickly and the
		 *    caller can stall after page list has been processed.
		 *
		 * 2) Global or new memcg reclaim encounters a page that is
		 *    not marked for immediate reclaim, or the caller does not
		 *    have __GFP_FS (or __GFP_IO if it's simply going to swap,
		 *    not to fs). In this case mark the page for immediate
		 *    reclaim and continue scanning.
		 *
		 *    Require may_enter_fs because we would wait on fs, which
		 *    may not have submitted IO yet. And the loop driver might
		 *    enter reclaim, and deadlock if it waits on a page for
		 *    which it is needed to do the write (loop masks off
		 *    __GFP_IO|__GFP_FS for this reason); but more thought
		 *    would probably show more reasons.
		 *
		 * 3) Legacy memcg encounters a page that is already marked
		 *    PageReclaim. memcg does not have any dirty pages
		 *    throttling so we could easily OOM just because too many
		 *    pages are in writeback and there is nothing else to
		 *    reclaim. Wait for the writeback to complete.
		 *
		 * In cases 1) and 2) we activate the pages to get them out of
		 * the way while we continue scanning for clean pages on the
		 * inactive list and refilling from the active list. The
		 * observation here is that waiting for disk writes is more
		 * expensive than potentially causing reloads down the line.
		 * Since they're marked for immediate reclaim, they won't put
		 * memory pressure on the cache working set any longer than it
		 * takes to write them to disk.
		 */
		if (PageWriteback(page)) {
			/* Case 1 above */
			if (current_is_kswapd() &&
			    PageReclaim(page) &&
			    test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
				nr_immediate++;
				goto activate_locked;

			/* Case 2 above */
			} else if (sane_reclaim(sc) ||
			    !PageReclaim(page) || !may_enter_fs) {
				/*
				 * This is slightly racy - end_page_writeback()
				 * might have just cleared PageReclaim, then
				 * setting PageReclaim here end up interpreted
				 * as PageReadahead - but that does not matter
				 * enough to care.  What we do want is for this
				 * page to have PageReclaim set next time memcg
				 * reclaim reaches the tests above, so it will
				 * then wait_on_page_writeback() to avoid OOM;
				 * and it's also appropriate in global reclaim.
				 */
				SetPageReclaim(page);
				nr_writeback++;
				goto activate_locked;

			/* Case 3 above */
			} else {
				unlock_page(page);
				wait_on_page_writeback(page);
				/* then go back and try same page again */
				list_add_tail(&page->lru, page_list);
				continue;
			}
		}

		if (!force_reclaim)
			references = page_check_references(page, sc);

		switch (references) {
		case PAGEREF_ACTIVATE:
			goto activate_locked;
		case PAGEREF_KEEP:
			nr_ref_keep++;
			goto keep_locked;
		case PAGEREF_RECLAIM:
		case PAGEREF_RECLAIM_CLEAN:
			; /* try to reclaim the page below */
		}

		/*
		 * Anonymous process memory has backing store?
		 * Try to allocate it some swap space here.
		 * Lazyfree page could be freed directly
		 */
		if (PageAnon(page) && PageSwapBacked(page)) {
			if (!PageSwapCache(page)) {
				if (!(sc->gfp_mask & __GFP_IO))
					goto keep_locked;
				if (PageTransHuge(page)) {
					/* cannot split THP, skip it */
					if (!can_split_huge_page(page, NULL))
						goto activate_locked;
					/*
					 * Split pages without a PMD map right
					 * away. Chances are some or all of the
					 * tail pages can be freed without IO.
					 */
					if (!compound_mapcount(page) &&
					    split_huge_page_to_list(page,
								    page_list))
						goto activate_locked;
				}
				if (!add_to_swap(page)) {
					if (!PageTransHuge(page))
						goto activate_locked;
					/* Fallback to swap normal pages */
					if (split_huge_page_to_list(page,
								    page_list))
						goto activate_locked;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
					count_vm_event(THP_SWPOUT_FALLBACK);
#endif
					if (!add_to_swap(page))
						goto activate_locked;
				}

				may_enter_fs = 1;

				/* Adding to swap updated mapping */
				mapping = page_mapping(page);
			}
		} else if (unlikely(PageTransHuge(page))) {
			/* Split file THP */
			if (split_huge_page_to_list(page, page_list))
				goto keep_locked;
		}

		/*
		 * The page is mapped into the page tables of one or more
		 * processes. Try to unmap it here.
		 */
		if (page_mapped(page)) {
			enum ttu_flags flags = ttu_flags | TTU_BATCH_FLUSH;

			if (unlikely(PageTransHuge(page)))
				flags |= TTU_SPLIT_HUGE_PMD;
			if (!try_to_unmap(page, flags)) {
				nr_unmap_fail++;
				goto activate_locked;
			}
		}

		if (PageDirty(page)) {
			/*
			 * Only kswapd can writeback filesystem pages
			 * to avoid risk of stack overflow. But avoid
			 * injecting inefficient single-page IO into
			 * flusher writeback as much as possible: only
			 * write pages when we've encountered many
			 * dirty pages, and when we've already scanned
			 * the rest of the LRU for clean pages and see
			 * the same dirty pages again (PageReclaim).
			 */
			if (page_is_file_cache(page) &&
			    (!current_is_kswapd() || !PageReclaim(page) ||
			     !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
				/*
				 * Immediately reclaim when written back.
				 * Similar in principal to deactivate_page()
				 * except we already have the page isolated
				 * and know it's dirty
				 */
				inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
				SetPageReclaim(page);

				goto activate_locked;
			}

			if (references == PAGEREF_RECLAIM_CLEAN)
				goto keep_locked;
			if (!may_enter_fs)
				goto keep_locked;
			if (!sc->may_writepage)
				goto keep_locked;

			/*
			 * Page is dirty. Flush the TLB if a writable entry
			 * potentially exists to avoid CPU writes after IO
			 * starts and then write it out here.
			 */
			try_to_unmap_flush_dirty();
			switch (pageout(page, mapping, sc)) {
			case PAGE_KEEP:
				goto keep_locked;
			case PAGE_ACTIVATE:
				goto activate_locked;
			case PAGE_SUCCESS:
				if (PageWriteback(page))
					goto keep;
				if (PageDirty(page))
					goto keep;

				/*
				 * A synchronous write - probably a ramdisk.  Go
				 * ahead and try to reclaim the page.
				 */
				if (!trylock_page(page))
					goto keep;
				if (PageDirty(page) || PageWriteback(page))
					goto keep_locked;
				mapping = page_mapping(page);
			case PAGE_CLEAN:
				; /* try to free the page below */
			}
		}

		/*
		 * If the page has buffers, try to free the buffer mappings
		 * associated with this page. If we succeed we try to free
		 * the page as well.
		 *
		 * We do this even if the page is PageDirty().
		 * try_to_release_page() does not perform I/O, but it is
		 * possible for a page to have PageDirty set, but it is actually
		 * clean (all its buffers are clean).  This happens if the
		 * buffers were written out directly, with submit_bh(). ext3
		 * will do this, as well as the blockdev mapping.
		 * try_to_release_page() will discover that cleanness and will
		 * drop the buffers and mark the page clean - it can be freed.
		 *
		 * Rarely, pages can have buffers and no ->mapping.  These are
		 * the pages which were not successfully invalidated in
		 * truncate_complete_page().  We try to drop those buffers here
		 * and if that worked, and the page is no longer mapped into
		 * process address space (page_count == 1) it can be freed.
		 * Otherwise, leave the page on the LRU so it is swappable.
		 */
		if (page_has_private(page)) {
			if (!try_to_release_page(page, sc->gfp_mask))
				goto activate_locked;
			if (!mapping && page_count(page) == 1) {
				unlock_page(page);
				if (put_page_testzero(page))
					goto free_it;
				else {
					/*
					 * rare race with speculative reference.
					 * the speculative reference will free
					 * this page shortly, so we may
					 * increment nr_reclaimed here (and
					 * leave it off the LRU).
					 */
					nr_reclaimed++;
					continue;
				}
			}
		}

		if (PageAnon(page) && !PageSwapBacked(page)) {
			/* follow __remove_mapping for reference */
			if (!page_ref_freeze(page, 1))
				goto keep_locked;
			if (PageDirty(page)) {
				page_ref_unfreeze(page, 1);
				goto keep_locked;
			}

			count_vm_event(PGLAZYFREED);
			count_memcg_page_event(page, PGLAZYFREED);
		} else if (!mapping || !__remove_mapping(mapping, page, true))
			goto keep_locked;
		/*
		 * At this point, we have no other references and there is
		 * no way to pick any more up (removed from LRU, removed
		 * from pagecache). Can use non-atomic bitops now (and
		 * we obviously don't have to worry about waking up a process
		 * waiting on the page lock, because there are no references.
		 */
		__ClearPageLocked(page);
free_it:
		nr_reclaimed++;

		/*
		 * Is there need to periodically free_page_list? It would
		 * appear not as the counts should be low
		 */
		if (unlikely(PageTransHuge(page))) {
			mem_cgroup_uncharge(page);
			(*get_compound_page_dtor(page))(page);
		} else
			list_add(&page->lru, &free_pages);
		continue;

activate_locked:
		/* Not a candidate for swapping, so reclaim swap space. */
		if (PageSwapCache(page) && (mem_cgroup_swap_full(page) ||
						PageMlocked(page)))
			try_to_free_swap(page);
		VM_BUG_ON_PAGE(PageActive(page), page);
		if (!PageMlocked(page)) {
			SetPageActive(page);
			pgactivate++;
			count_memcg_page_event(page, PGACTIVATE);
		}
keep_locked:
		unlock_page(page);
keep:
		list_add(&page->lru, &ret_pages);
		VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
	}

	mem_cgroup_uncharge_list(&free_pages);
	try_to_unmap_flush();
	free_hot_cold_page_list(&free_pages, true);

	list_splice(&ret_pages, page_list);
	count_vm_events(PGACTIVATE, pgactivate);

	if (stat) {
		stat->nr_dirty = nr_dirty;
		stat->nr_congested = nr_congested;
		stat->nr_unqueued_dirty = nr_unqueued_dirty;
		stat->nr_writeback = nr_writeback;
		stat->nr_immediate = nr_immediate;
		stat->nr_activate = pgactivate;
		stat->nr_ref_keep = nr_ref_keep;
		stat->nr_unmap_fail = nr_unmap_fail;
	}
	return nr_reclaimed;
}

unsigned long reclaim_clean_pages_from_list(struct zone *zone,
					    struct list_head *page_list)
{
	struct scan_control sc = {
		.gfp_mask = GFP_KERNEL,
		.priority = DEF_PRIORITY,
		.may_unmap = 1,
	};
	unsigned long ret;
	struct page *page, *next;
	LIST_HEAD(clean_pages);

	list_for_each_entry_safe(page, next, page_list, lru) {
		if (page_is_file_cache(page) && !PageDirty(page) &&
		    !__PageMovable(page)) {
			ClearPageActive(page);
			list_move(&page->lru, &clean_pages);
		}
	}

	ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
			TTU_IGNORE_ACCESS, NULL, true);
	list_splice(&clean_pages, page_list);
	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret);
	return ret;
}

/*
 * Attempt to remove the specified page from its LRU.  Only take this page
 * if it is of the appropriate PageActive status.  Pages which are being
 * freed elsewhere are also ignored.
 *
 * page:	page to consider
 * mode:	one of the LRU isolation modes defined above
 *
 * returns 0 on success, -ve errno on failure.
 */
int __isolate_lru_page(struct page *page, isolate_mode_t mode)
{
	int ret = -EINVAL;

	/* Only take pages on the LRU. */
	if (!PageLRU(page))
		return ret;

	/* Compaction should not handle unevictable pages but CMA can do so */
	if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
		return ret;

	ret = -EBUSY;

	/*
	 * To minimise LRU disruption, the caller can indicate that it only
	 * wants to isolate pages it will be able to operate on without
	 * blocking - clean pages for the most part.
	 *
	 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
	 * that it is possible to migrate without blocking
	 */
	if (mode & ISOLATE_ASYNC_MIGRATE) {
		/* All the caller can do on PageWriteback is block */
		if (PageWriteback(page))
			return ret;

		if (PageDirty(page)) {
			struct address_space *mapping;

			/*
			 * Only pages without mappings or that have a
			 * ->migratepage callback are possible to migrate
			 * without blocking
			 */
			mapping = page_mapping(page);
			if (mapping && !mapping->a_ops->migratepage)
				return ret;
		}
	}

	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
		return ret;

	if (likely(get_page_unless_zero(page))) {
		/*
		 * Be careful not to clear PageLRU until after we're
		 * sure the page is not being freed elsewhere -- the
		 * page release code relies on it.
		 */
		ClearPageLRU(page);
		ret = 0;
	}

	return ret;
}


/*
 * Update LRU sizes after isolating pages. The LRU size updates must
 * be complete before mem_cgroup_update_lru_size due to a santity check.
 */
static __always_inline void update_lru_sizes(struct lruvec *lruvec,
			enum lru_list lru, unsigned long *nr_zone_taken)
{
	int zid;

	for (zid = 0; zid < MAX_NR_ZONES; zid++) {
		if (!nr_zone_taken[zid])
			continue;

		__update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
#ifdef CONFIG_MEMCG
		mem_cgroup_update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
#endif
	}

}

/*
 * zone_lru_lock is heavily contended.  Some of the functions that
 * shrink the lists perform better by taking out a batch of pages
 * and working on them outside the LRU lock.
 *
 * For pagecache intensive workloads, this function is the hottest
 * spot in the kernel (apart from copy_*_user functions).
 *
 * Appropriate locks must be held before calling this function.
 *
 * @nr_to_scan:	The number of eligible pages to look through on the list.
 * @lruvec:	The LRU vector to pull pages from.
 * @dst:	The temp list to put pages on to.
 * @nr_scanned:	The number of pages that were scanned.
 * @sc:		The scan_control struct for this reclaim session
 * @mode:	One of the LRU isolation modes
 * @lru:	LRU list id for isolating
 *
 * returns how many pages were moved onto *@dst.
 */
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
		struct lruvec *lruvec, struct list_head *dst,
		unsigned long *nr_scanned, struct scan_control *sc,
		isolate_mode_t mode, enum lru_list lru)
{
	struct list_head *src = &lruvec->lists[lru];
	unsigned long nr_taken = 0;
	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
	unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
	unsigned long skipped = 0;
	unsigned long scan, total_scan, nr_pages;
	LIST_HEAD(pages_skipped);

	scan = 0;
	for (total_scan = 0;
	     scan < nr_to_scan && nr_taken < nr_to_scan && !list_empty(src);
	     total_scan++) {
		struct page *page;

		page = lru_to_page(src);
		prefetchw_prev_lru_page(page, src, flags);

		VM_BUG_ON_PAGE(!PageLRU(page), page);

		if (page_zonenum(page) > sc->reclaim_idx) {
			list_move(&page->lru, &pages_skipped);
			nr_skipped[page_zonenum(page)]++;
			continue;
		}

		/*
		 * Do not count skipped pages because that makes the function
		 * return with no isolated pages if the LRU mostly contains
		 * ineligible pages.  This causes the VM to not reclaim any
		 * pages, triggering a premature OOM.
		 */
		scan++;
		switch (__isolate_lru_page(page, mode)) {
		case 0:
			nr_pages = hpage_nr_pages(page);
			nr_taken += nr_pages;
			nr_zone_taken[page_zonenum(page)] += nr_pages;
			list_move(&page->lru, dst);
			break;

		case -EBUSY:
			/* else it is being freed elsewhere */
			list_move(&page->lru, src);
			continue;

		default:
			BUG();
		}
	}

	/*
	 * Splice any skipped pages to the start of the LRU list. Note that
	 * this disrupts the LRU order when reclaiming for lower zones but
	 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
	 * scanning would soon rescan the same pages to skip and put the
	 * system at risk of premature OOM.
	 */
	if (!list_empty(&pages_skipped)) {
		int zid;

		list_splice(&pages_skipped, src);
		for (zid = 0; zid < MAX_NR_ZONES; zid++) {
			if (!nr_skipped[zid])
				continue;

			__count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
			skipped += nr_skipped[zid];
		}
	}
	*nr_scanned = total_scan;
	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
				    total_scan, skipped, nr_taken, mode, lru);
	update_lru_sizes(lruvec, lru, nr_zone_taken);
	return nr_taken;
}

/**
 * isolate_lru_page - tries to isolate a page from its LRU list
 * @page: page to isolate from its LRU list
 *
 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
 * vmstat statistic corresponding to whatever LRU list the page was on.
 *
 * Returns 0 if the page was removed from an LRU list.
 * Returns -EBUSY if the page was not on an LRU list.
 *
 * The returned page will have PageLRU() cleared.  If it was found on
 * the active list, it will have PageActive set.  If it was found on
 * the unevictable list, it will have the PageUnevictable bit set. That flag
 * may need to be cleared by the caller before letting the page go.
 *
 * The vmstat statistic corresponding to the list on which the page was
 * found will be decremented.
 *
 * Restrictions:
 * (1) Must be called with an elevated refcount on the page. This is a
 *     fundamentnal difference from isolate_lru_pages (which is called
 *     without a stable reference).
 * (2) the lru_lock must not be held.
 * (3) interrupts must be enabled.
 */
int isolate_lru_page(struct page *page)
{
	int ret = -EBUSY;

	VM_BUG_ON_PAGE(!page_count(page), page);
	WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");

	if (PageLRU(page)) {
		struct zone *zone = page_zone(page);
		struct lruvec *lruvec;

		spin_lock_irq(zone_lru_lock(zone));
		lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
		if (PageLRU(page)) {
			int lru = page_lru(page);
			get_page(page);
			ClearPageLRU(page);
			del_page_from_lru_list(page, lruvec, lru);
			ret = 0;
		}
		spin_unlock_irq(zone_lru_lock(zone));
	}
	return ret;
}

/*
 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
 * then get resheduled. When there are massive number of tasks doing page
 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
 * the LRU list will go small and be scanned faster than necessary, leading to
 * unnecessary swapping, thrashing and OOM.
 */
static int too_many_isolated(struct pglist_data *pgdat, int file,
		struct scan_control *sc)
{
	unsigned long inactive, isolated;

	if (current_is_kswapd())
		return 0;

	if (!sane_reclaim(sc))
		return 0;

	if (file) {
		inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
		isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
	} else {
		inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
		isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
	}

	/*
	 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
	 * won't get blocked by normal direct-reclaimers, forming a circular
	 * deadlock.
	 */
	if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
		inactive >>= 3;

	return isolated > inactive;
}

static noinline_for_stack void
putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
{
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
	LIST_HEAD(pages_to_free);

	/*
	 * Put back any unfreeable pages.
	 */
	while (!list_empty(page_list)) {
		struct page *page = lru_to_page(page_list);
		int lru;

		VM_BUG_ON_PAGE(PageLRU(page), page);
		list_del(&page->lru);
		if (unlikely(!page_evictable(page))) {
			spin_unlock_irq(&pgdat->lru_lock);
			putback_lru_page(page);
			spin_lock_irq(&pgdat->lru_lock);
			continue;
		}

		lruvec = mem_cgroup_page_lruvec(page, pgdat);

		SetPageLRU(page);
		lru = page_lru(page);
		add_page_to_lru_list(page, lruvec, lru);

		if (is_active_lru(lru)) {
			int file = is_file_lru(lru);
			int numpages = hpage_nr_pages(page);
			reclaim_stat->recent_rotated[file] += numpages;
		}
		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
			del_page_from_lru_list(page, lruvec, lru);

			if (unlikely(PageCompound(page))) {
				spin_unlock_irq(&pgdat->lru_lock);
				mem_cgroup_uncharge(page);
				(*get_compound_page_dtor(page))(page);
				spin_lock_irq(&pgdat->lru_lock);
			} else
				list_add(&page->lru, &pages_to_free);
		}
	}

	/*
	 * To save our caller's stack, now use input list for pages to free.
	 */
	list_splice(&pages_to_free, page_list);
}

/*
 * If a kernel thread (such as nfsd for loop-back mounts) services
 * a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
 * In that case we should only throttle if the backing device it is
 * writing to is congested.  In other cases it is safe to throttle.
 */
static int current_may_throttle(void)
{
	return !(current->flags & PF_LESS_THROTTLE) ||
		current->backing_dev_info == NULL ||
		bdi_write_congested(current->backing_dev_info);
}

/*
 * shrink_inactive_list() is a helper for shrink_node().  It returns the number
 * of reclaimed pages
 */
static noinline_for_stack unsigned long
shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
		     struct scan_control *sc, enum lru_list lru)
{
	LIST_HEAD(page_list);
	unsigned long nr_scanned;
	unsigned long nr_reclaimed = 0;
	unsigned long nr_taken;
	struct reclaim_stat stat = {};
	isolate_mode_t isolate_mode = 0;
	int file = is_file_lru(lru);
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
	bool stalled = false;

	while (unlikely(too_many_isolated(pgdat, file, sc))) {
		if (stalled)
			return 0;

		/* wait a bit for the reclaimer. */
		msleep(100);
		stalled = true;

		/* We are about to die and free our memory. Return now. */
		if (fatal_signal_pending(current))
			return SWAP_CLUSTER_MAX;
	}

	lru_add_drain();

	if (!sc->may_unmap)
		isolate_mode |= ISOLATE_UNMAPPED;

	spin_lock_irq(&pgdat->lru_lock);

	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
				     &nr_scanned, sc, isolate_mode, lru);

	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
	reclaim_stat->recent_scanned[file] += nr_taken;

	if (current_is_kswapd()) {
		if (global_reclaim(sc))
			__count_vm_events(PGSCAN_KSWAPD, nr_scanned);
		count_memcg_events(lruvec_memcg(lruvec), PGSCAN_KSWAPD,
				   nr_scanned);
	} else {
		if (global_reclaim(sc))
			__count_vm_events(PGSCAN_DIRECT, nr_scanned);
		count_memcg_events(lruvec_memcg(lruvec), PGSCAN_DIRECT,
				   nr_scanned);
	}
	spin_unlock_irq(&pgdat->lru_lock);

	if (nr_taken == 0)
		return 0;

	nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, 0,
				&stat, false);

	spin_lock_irq(&pgdat->lru_lock);

	if (current_is_kswapd()) {
		if (global_reclaim(sc))
			__count_vm_events(PGSTEAL_KSWAPD, nr_reclaimed);
		count_memcg_events(lruvec_memcg(lruvec), PGSTEAL_KSWAPD,
				   nr_reclaimed);
	} else {
		if (global_reclaim(sc))
			__count_vm_events(PGSTEAL_DIRECT, nr_reclaimed);
		count_memcg_events(lruvec_memcg(lruvec), PGSTEAL_DIRECT,
				   nr_reclaimed);
	}

	putback_inactive_pages(lruvec, &page_list);

	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);

	spin_unlock_irq(&pgdat->lru_lock);

	mem_cgroup_uncharge_list(&page_list);
	free_hot_cold_page_list(&page_list, true);

	/*
	 * If reclaim is isolating dirty pages under writeback, it implies
	 * that the long-lived page allocation rate is exceeding the page
	 * laundering rate. Either the global limits are not being effective
	 * at throttling processes due to the page distribution throughout
	 * zones or there is heavy usage of a slow backing device. The
	 * only option is to throttle from reclaim context which is not ideal
	 * as there is no guarantee the dirtying process is throttled in the
	 * same way balance_dirty_pages() manages.
	 *
	 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
	 * of pages under pages flagged for immediate reclaim and stall if any
	 * are encountered in the nr_immediate check below.
	 */
	if (stat.nr_writeback && stat.nr_writeback == nr_taken)
		set_bit(PGDAT_WRITEBACK, &pgdat->flags);

	/*
	 * Legacy memcg will stall in page writeback so avoid forcibly
	 * stalling here.
	 */
	if (sane_reclaim(sc)) {
		/*
		 * Tag a zone as congested if all the dirty pages scanned were
		 * backed by a congested BDI and wait_iff_congested will stall.
		 */
		if (stat.nr_dirty && stat.nr_dirty == stat.nr_congested)
			set_bit(PGDAT_CONGESTED, &pgdat->flags);

		/*
		 * If dirty pages are scanned that are not queued for IO, it
		 * implies that flushers are not doing their job. This can
		 * happen when memory pressure pushes dirty pages to the end of
		 * the LRU before the dirty limits are breached and the dirty
		 * data has expired. It can also happen when the proportion of
		 * dirty pages grows not through writes but through memory
		 * pressure reclaiming all the clean cache. And in some cases,
		 * the flushers simply cannot keep up with the allocation
		 * rate. Nudge the flusher threads in case they are asleep, but
		 * also allow kswapd to start writing pages during reclaim.
		 */
		if (stat.nr_unqueued_dirty == nr_taken) {
			wakeup_flusher_threads(WB_REASON_VMSCAN);
			set_bit(PGDAT_DIRTY, &pgdat->flags);
		}

		/*
		 * If kswapd scans pages marked marked for immediate
		 * reclaim and under writeback (nr_immediate), it implies
		 * that pages are cycling through the LRU faster than
		 * they are written so also forcibly stall.
		 */
		if (stat.nr_immediate && current_may_throttle())
			congestion_wait(BLK_RW_ASYNC, HZ/10);
	}

	/*
	 * Stall direct reclaim for IO completions if underlying BDIs or zone
	 * is congested. Allow kswapd to continue until it starts encountering
	 * unqueued dirty pages or cycling through the LRU too quickly.
	 */
	if (!sc->hibernation_mode && !current_is_kswapd() &&
	    current_may_throttle())
		wait_iff_congested(pgdat, BLK_RW_ASYNC, HZ/10);

	trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
			nr_scanned, nr_reclaimed,
			stat.nr_dirty,  stat.nr_writeback,
			stat.nr_congested, stat.nr_immediate,
			stat.nr_activate, stat.nr_ref_keep,
			stat.nr_unmap_fail,
			sc->priority, file);
	return nr_reclaimed;
}

/*
 * This moves pages from the active list to the inactive list.
 *
 * We move them the other way if the page is referenced by one or more
 * processes, from rmap.
 *
 * If the pages are mostly unmapped, the processing is fast and it is
 * appropriate to hold zone_lru_lock across the whole operation.  But if
 * the pages are mapped, the processing is slow (page_referenced()) so we
 * should drop zone_lru_lock around each page.  It's impossible to balance
 * this, so instead we remove the pages from the LRU while processing them.
 * It is safe to rely on PG_active against the non-LRU pages in here because
 * nobody will play with that bit on a non-LRU page.
 *
 * The downside is that we have to touch page->_refcount against each page.
 * But we had to alter page->flags anyway.
 *
 * Returns the number of pages moved to the given lru.
 */

static unsigned move_active_pages_to_lru(struct lruvec *lruvec,
				     struct list_head *list,
				     struct list_head *pages_to_free,
				     enum lru_list lru)
{
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
	struct page *page;
	int nr_pages;
	int nr_moved = 0;

	while (!list_empty(list)) {
		page = lru_to_page(list);
		lruvec = mem_cgroup_page_lruvec(page, pgdat);

		VM_BUG_ON_PAGE(PageLRU(page), page);
		SetPageLRU(page);

		nr_pages = hpage_nr_pages(page);
		update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
		list_move(&page->lru, &lruvec->lists[lru]);

		if (put_page_testzero(page)) {
			__ClearPageLRU(page);
			__ClearPageActive(page);
			del_page_from_lru_list(page, lruvec, lru);

			if (unlikely(PageCompound(page))) {
				spin_unlock_irq(&pgdat->lru_lock);
				mem_cgroup_uncharge(page);
				(*get_compound_page_dtor(page))(page);
				spin_lock_irq(&pgdat->lru_lock);
			} else
				list_add(&page->lru, pages_to_free);
		} else {
			nr_moved += nr_pages;
		}
	}

	if (!is_active_lru(lru)) {
		__count_vm_events(PGDEACTIVATE, nr_moved);
		count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
				   nr_moved);
	}

	return nr_moved;
}

static void shrink_active_list(unsigned long nr_to_scan,
			       struct lruvec *lruvec,
			       struct scan_control *sc,
			       enum lru_list lru)
{
	unsigned long nr_taken;
	unsigned long nr_scanned;
	unsigned long vm_flags;
	LIST_HEAD(l_hold);	/* The pages which were snipped off */
	LIST_HEAD(l_active);
	LIST_HEAD(l_inactive);
	struct page *page;
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
	unsigned nr_deactivate, nr_activate;
	unsigned nr_rotated = 0;
	isolate_mode_t isolate_mode = 0;
	int file = is_file_lru(lru);
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);

	lru_add_drain();

	if (!sc->may_unmap)
		isolate_mode |= ISOLATE_UNMAPPED;

	spin_lock_irq(&pgdat->lru_lock);

	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
				     &nr_scanned, sc, isolate_mode, lru);

	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
	reclaim_stat->recent_scanned[file] += nr_taken;

	__count_vm_events(PGREFILL, nr_scanned);
	count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned);

	spin_unlock_irq(&pgdat->lru_lock);

	while (!list_empty(&l_hold)) {
		cond_resched();
		page = lru_to_page(&l_hold);
		list_del(&page->lru);

		if (unlikely(!page_evictable(page))) {
			putback_lru_page(page);
			continue;
		}

		if (unlikely(buffer_heads_over_limit)) {
			if (page_has_private(page) && trylock_page(page)) {
				if (page_has_private(page))
					try_to_release_page(page, 0);
				unlock_page(page);
			}
		}

		if (page_referenced(page, 0, sc->target_mem_cgroup,
				    &vm_flags)) {
			nr_rotated += hpage_nr_pages(page);
			/*
			 * Identify referenced, file-backed active pages and
			 * give them one more trip around the active list. So
			 * that executable code get better chances to stay in
			 * memory under moderate memory pressure.  Anon pages
			 * are not likely to be evicted by use-once streaming
			 * IO, plus JVM can create lots of anon VM_EXEC pages,
			 * so we ignore them here.
			 */
			if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
				list_add(&page->lru, &l_active);
				continue;
			}
		}

		ClearPageActive(page);	/* we are de-activating */
		list_add(&page->lru, &l_inactive);
	}

	/*
	 * Move pages back to the lru list.
	 */
	spin_lock_irq(&pgdat->lru_lock);
	/*
	 * Count referenced pages from currently used mappings as rotated,
	 * even though only some of them are actually re-activated.  This
	 * helps balance scan pressure between file and anonymous pages in
	 * get_scan_count.
	 */
	reclaim_stat->recent_rotated[file] += nr_rotated;

	nr_activate = move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
	nr_deactivate = move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
	spin_unlock_irq(&pgdat->lru_lock);

	mem_cgroup_uncharge_list(&l_hold);
	free_hot_cold_page_list(&l_hold, true);
	trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
			nr_deactivate, nr_rotated, sc->priority, file);
}

/*
 * The inactive anon list should be small enough that the VM never has
 * to do too much work.
 *
 * The inactive file list should be small enough to leave most memory
 * to the established workingset on the scan-resistant active list,
 * but large enough to avoid thrashing the aggregate readahead window.
 *
 * Both inactive lists should also be large enough that each inactive
 * page has a chance to be referenced again before it is reclaimed.
 *
 * If that fails and refaulting is observed, the inactive list grows.
 *
 * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
 * on this LRU, maintained by the pageout code. A zone->inactive_ratio
 * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
 *
 * total     target    max
 * memory    ratio     inactive
 * -------------------------------------
 *   10MB       1         5MB
 *  100MB       1        50MB
 *    1GB       3       250MB
 *   10GB      10       0.9GB
 *  100GB      31         3GB
 *    1TB     101        10GB
 *   10TB     320        32GB
 */
static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
				 struct mem_cgroup *memcg,
				 struct scan_control *sc, bool actual_reclaim)
{
	enum lru_list active_lru = file * LRU_FILE + LRU_ACTIVE;
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
	enum lru_list inactive_lru = file * LRU_FILE;
	unsigned long inactive, active;
	unsigned long inactive_ratio;
	unsigned long refaults;
	unsigned long gb;

	/*
	 * If we don't have swap space, anonymous page deactivation
	 * is pointless.
	 */
	if (!file && !total_swap_pages)
		return false;

	inactive = lruvec_lru_size(lruvec, inactive_lru, sc->reclaim_idx);
	active = lruvec_lru_size(lruvec, active_lru, sc->reclaim_idx);

	if (memcg)
		refaults = memcg_page_state(memcg, WORKINGSET_ACTIVATE);
	else
		refaults = node_page_state(pgdat, WORKINGSET_ACTIVATE);

	/*
	 * When refaults are being observed, it means a new workingset
	 * is being established. Disable active list protection to get
	 * rid of the stale workingset quickly.
	 */
	if (file && actual_reclaim && lruvec->refaults != refaults) {
		inactive_ratio = 0;
	} else {
		gb = (inactive + active) >> (30 - PAGE_SHIFT);
		if (gb)
			inactive_ratio = int_sqrt(10 * gb);
		else
			inactive_ratio = 1;
	}

	if (actual_reclaim)
		trace_mm_vmscan_inactive_list_is_low(pgdat->node_id, sc->reclaim_idx,
			lruvec_lru_size(lruvec, inactive_lru, MAX_NR_ZONES), inactive,
			lruvec_lru_size(lruvec, active_lru, MAX_NR_ZONES), active,
			inactive_ratio, file);

	return inactive * inactive_ratio < active;
}

static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
				 struct lruvec *lruvec, struct mem_cgroup *memcg,
				 struct scan_control *sc)
{
	if (is_active_lru(lru)) {
		if (inactive_list_is_low(lruvec, is_file_lru(lru),
					 memcg, sc, true))
			shrink_active_list(nr_to_scan, lruvec, sc, lru);
		return 0;
	}

	return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
}

enum scan_balance {
	SCAN_EQUAL,
	SCAN_FRACT,
	SCAN_ANON,
	SCAN_FILE,
};

/*
 * Determine how aggressively the anon and file LRU lists should be
 * scanned.  The relative value of each set of LRU lists is determined
 * by looking at the fraction of the pages scanned we did rotate back
 * onto the active list instead of evict.
 *
 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
 */
static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
			   struct scan_control *sc, unsigned long *nr,
			   unsigned long *lru_pages)
{
	int swappiness = mem_cgroup_swappiness(memcg);
	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
	u64 fraction[2];
	u64 denominator = 0;	/* gcc */
	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
	unsigned long anon_prio, file_prio;
	enum scan_balance scan_balance;
	unsigned long anon, file;
	unsigned long ap, fp;
	enum lru_list lru;

	/* If we have no swap space, do not bother scanning anon pages. */
	if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
		scan_balance = SCAN_FILE;
		goto out;
	}

	/*
	 * Global reclaim will swap to prevent OOM even with no
	 * swappiness, but memcg users want to use this knob to
	 * disable swapping for individual groups completely when
	 * using the memory controller's swap limit feature would be
	 * too expensive.
	 */
	if (!global_reclaim(sc) && !swappiness) {
		scan_balance = SCAN_FILE;
		goto out;
	}

	/*
	 * Do not apply any pressure balancing cleverness when the
	 * system is close to OOM, scan both anon and file equally
	 * (unless the swappiness setting disagrees with swapping).
	 */
	if (!sc->priority && swappiness) {
		scan_balance = SCAN_EQUAL;
		goto out;
	}

	/*
	 * Prevent the reclaimer from falling into the cache trap: as
	 * cache pages start out inactive, every cache fault will tip
	 * the scan balance towards the file LRU.  And as the file LRU
	 * shrinks, so does the window for rotation from references.
	 * This means we have a runaway feedback loop where a tiny
	 * thrashing file LRU becomes infinitely more attractive than
	 * anon pages.  Try to detect this based on file LRU size.
	 */
	if (global_reclaim(sc)) {
		unsigned long pgdatfile;
		unsigned long pgdatfree;
		int z;
		unsigned long total_high_wmark = 0;

		pgdatfree = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
		pgdatfile = node_page_state(pgdat, NR_ACTIVE_FILE) +
			   node_page_state(pgdat, NR_INACTIVE_FILE);

		for (z = 0; z < MAX_NR_ZONES; z++) {
			struct zone *zone = &pgdat->node_zones[z];
			if (!managed_zone(zone))
				continue;

			total_high_wmark += high_wmark_pages(zone);
		}

		if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
			/*
			 * Force SCAN_ANON if there are enough inactive
			 * anonymous pages on the LRU in eligible zones.
			 * Otherwise, the small LRU gets thrashed.
			 */
			if (!inactive_list_is_low(lruvec, false, memcg, sc, false) &&
			    lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, sc->reclaim_idx)
					>> sc->priority) {
				scan_balance = SCAN_ANON;
				goto out;
			}
		}
	}

	/*
	 * If there is enough inactive page cache, i.e. if the size of the
	 * inactive list is greater than that of the active list *and* the
	 * inactive list actually has some pages to scan on this priority, we
	 * do not reclaim anything from the anonymous working set right now.
	 * Without the second condition we could end up never scanning an
	 * lruvec even if it has plenty of old anonymous pages unless the
	 * system is under heavy pressure.
	 */
	if (!inactive_list_is_low(lruvec, true, memcg, sc, false) &&
	    lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, sc->reclaim_idx) >> sc->priority) {
		scan_balance = SCAN_FILE;
		goto out;
	}

	scan_balance = SCAN_FRACT;

	/*
	 * With swappiness at 100, anonymous and file have the same priority.
	 * This scanning priority is essentially the inverse of IO cost.
	 */
	anon_prio = swappiness;
	file_prio = 200 - anon_prio;

	/*
	 * OK, so we have swap space and a fair amount of page cache
	 * pages.  We use the recently rotated / recently scanned
	 * ratios to determine how valuable each cache is.
	 *
	 * Because workloads change over time (and to avoid overflow)
	 * we keep these statistics as a floating average, which ends
	 * up weighing recent references more than old ones.
	 *
	 * anon in [0], file in [1]
	 */

	anon  = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON, MAX_NR_ZONES) +
		lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, MAX_NR_ZONES);
	file  = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES) +
		lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES);

	spin_lock_irq(&pgdat->lru_lock);
	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
		reclaim_stat->recent_scanned[0] /= 2;
		reclaim_stat->recent_rotated[0] /= 2;
	}

	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
		reclaim_stat->recent_scanned[1] /= 2;
		reclaim_stat->recent_rotated[1] /= 2;
	}

	/*
	 * The amount of pressure on anon vs file pages is inversely
	 * proportional to the fraction of recently scanned pages on
	 * each list that were recently referenced and in active use.
	 */
	ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
	ap /= reclaim_stat->recent_rotated[0] + 1;

	fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
	fp /= reclaim_stat->recent_rotated[1] + 1;
	spin_unlock_irq(&pgdat->lru_lock);

	fraction[0] = ap;
	fraction[1] = fp;
	denominator = ap + fp + 1;
out:
	*lru_pages = 0;
	for_each_evictable_lru(lru) {
		int file = is_file_lru(lru);
		unsigned long size;
		unsigned long scan;

		size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
		scan = size >> sc->priority;
		/*
		 * If the cgroup's already been deleted, make sure to
		 * scrape out the remaining cache.
		 */
		if (!scan && !mem_cgroup_online(memcg))
			scan = min(size, SWAP_CLUSTER_MAX);

		switch (scan_balance) {
		case SCAN_EQUAL:
			/* Scan lists relative to size */
			break;
		case SCAN_FRACT:
			/*
			 * Scan types proportional to swappiness and
			 * their relative recent reclaim efficiency.
			 */
			scan = div64_u64(scan * fraction[file],
					 denominator);
			break;
		case SCAN_FILE:
		case SCAN_ANON:
			/* Scan one type exclusively */
			if ((scan_balance == SCAN_FILE) != file) {
				size = 0;
				scan = 0;
			}
			break;
		default:
			/* Look ma, no brain */
			BUG();
		}

		*lru_pages += size;
		nr[lru] = scan;
	}
}

/*
 * This is a basic per-node page freer.  Used by both kswapd and direct reclaim.
 */
static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memcg,
			      struct scan_control *sc, unsigned long *lru_pages)
{
	struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
	unsigned long nr[NR_LRU_LISTS];
	unsigned long targets[NR_LRU_LISTS];
	unsigned long nr_to_scan;
	enum lru_list lru;
	unsigned long nr_reclaimed = 0;
	unsigned long nr_to_reclaim = sc->nr_to_reclaim;
	struct blk_plug plug;
	bool scan_adjusted;

	get_scan_count(lruvec, memcg, sc, nr, lru_pages);

	/* Record the original scan target for proportional adjustments later */
	memcpy(targets, nr, sizeof(nr));

	/*
	 * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
	 * event that can occur when there is little memory pressure e.g.
	 * multiple streaming readers/writers. Hence, we do not abort scanning
	 * when the requested number of pages are reclaimed when scanning at
	 * DEF_PRIORITY on the assumption that the fact we are direct
	 * reclaiming implies that kswapd is not keeping up and it is best to
	 * do a batch of work at once. For memcg reclaim one check is made to
	 * abort proportional reclaim if either the file or anon lru has already
	 * dropped to zero at the first pass.
	 */
	scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
			 sc->priority == DEF_PRIORITY);

	blk_start_plug(&plug);
	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
					nr[LRU_INACTIVE_FILE]) {
		unsigned long nr_anon, nr_file, percentage;
		unsigned long nr_scanned;

		for_each_evictable_lru(lru) {
			if (nr[lru]) {
				nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
				nr[lru] -= nr_to_scan;

				nr_reclaimed += shrink_list(lru, nr_to_scan,
							    lruvec, memcg, sc);
			}
		}

		cond_resched();

		if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
			continue;

		/*
		 * For kswapd and memcg, reclaim at least the number of pages
		 * requested. Ensure that the anon and file LRUs are scanned
		 * proportionally what was requested by get_scan_count(). We
		 * stop reclaiming one LRU and reduce the amount scanning
		 * proportional to the original scan target.
		 */
		nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
		nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];

		/*
		 * It's just vindictive to attack the larger once the smaller
		 * has gone to zero.  And given the way we stop scanning the
		 * smaller below, this makes sure that we only make one nudge
		 * towards proportionality once we've got nr_to_reclaim.
		 */
		if (!nr_file || !nr_anon)
			break;

		if (nr_file > nr_anon) {
			unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
						targets[LRU_ACTIVE_ANON] + 1;
			lru = LRU_BASE;
			percentage = nr_anon * 100 / scan_target;
		} else {
			unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
						targets[LRU_ACTIVE_FILE] + 1;
			lru = LRU_FILE;
			percentage = nr_file * 100 / scan_target;
		}

		/* Stop scanning the smaller of the LRU */
		nr[lru] = 0;
		nr[lru + LRU_ACTIVE] = 0;

		/*
		 * Recalculate the other LRU scan count based on its original
		 * scan target and the percentage scanning already complete
		 */
		lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
		nr_scanned = targets[lru] - nr[lru];
		nr[lru] = targets[lru] * (100 - percentage) / 100;
		nr[lru] -= min(nr[lru], nr_scanned);

		lru += LRU_ACTIVE;
		nr_scanned = targets[lru] - nr[lru];
		nr[lru] = targets[lru] * (100 - percentage) / 100;
		nr[lru] -= min(nr[lru], nr_scanned);

		scan_adjusted = true;
	}
	blk_finish_plug(&plug);
	sc->nr_reclaimed += nr_reclaimed;

	/*
	 * Even if we did not try to evict anon pages at all, we want to
	 * rebalance the anon lru active/inactive ratio.
	 */
	if (inactive_list_is_low(lruvec, false, memcg, sc, true))
		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
				   sc, LRU_ACTIVE_ANON);
}

/* Use reclaim/compaction for costly allocs or under memory pressure */
static bool in_reclaim_compaction(struct scan_control *sc)
{
	if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
			(sc->order > PAGE_ALLOC_COSTLY_ORDER ||
			 sc->priority < DEF_PRIORITY - 2))
		return true;

	return false;
}

/*
 * Reclaim/compaction is used for high-order allocation requests. It reclaims
 * order-0 pages before compacting the zone. should_continue_reclaim() returns
 * true if more pages should be reclaimed such that when the page allocator
 * calls try_to_compact_zone() that it will have enough free pages to succeed.
 * It will give up earlier than that if there is difficulty reclaiming pages.
 */
static inline bool should_continue_reclaim(struct pglist_data *pgdat,
					unsigned long nr_reclaimed,
					unsigned long nr_scanned,
					struct scan_control *sc)
{
	unsigned long pages_for_compaction;
	unsigned long inactive_lru_pages;
	int z;

	/* If not in reclaim/compaction mode, stop */
	if (!in_reclaim_compaction(sc))
		return false;

	/* Consider stopping depending on scan and reclaim activity */
	if (sc->gfp_mask & __GFP_RETRY_MAYFAIL) {
		/*
		 * For __GFP_RETRY_MAYFAIL allocations, stop reclaiming if the
		 * full LRU list has been scanned and we are still failing
		 * to reclaim pages. This full LRU scan is potentially
		 * expensive but a __GFP_RETRY_MAYFAIL caller really wants to succeed
		 */
		if (!nr_reclaimed && !nr_scanned)
			return false;
	} else {
		/*
		 * For non-__GFP_RETRY_MAYFAIL allocations which can presumably
		 * fail without consequence, stop if we failed to reclaim
		 * any pages from the last SWAP_CLUSTER_MAX number of
		 * pages that were scanned. This will return to the
		 * caller faster at the risk reclaim/compaction and
		 * the resulting allocation attempt fails
		 */
		if (!nr_reclaimed)
			return false;
	}

	/*
	 * If we have not reclaimed enough pages for compaction and the
	 * inactive lists are large enough, continue reclaiming
	 */
	pages_for_compaction = compact_gap(sc->order);
	inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
	if (get_nr_swap_pages() > 0)
		inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
	if (sc->nr_reclaimed < pages_for_compaction &&
			inactive_lru_pages > pages_for_compaction)
		return true;

	/* If compaction would go ahead or the allocation would succeed, stop */
	for (z = 0; z <= sc->reclaim_idx; z++) {
		struct zone *zone = &pgdat->node_zones[z];
		if (!managed_zone(zone))
			continue;

		switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
		case COMPACT_SUCCESS:
		case COMPACT_CONTINUE:
			return false;
		default:
			/* check next zone */
			;
		}
	}
	return true;
}

static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
{
	struct reclaim_state *reclaim_state = current->reclaim_state;
	unsigned long nr_reclaimed, nr_scanned;
	bool reclaimable = false;

	do {
		struct mem_cgroup *root = sc->target_mem_cgroup;
		struct mem_cgroup_reclaim_cookie reclaim = {
			.pgdat = pgdat,
			.priority = sc->priority,
		};
		unsigned long node_lru_pages = 0;
		struct mem_cgroup *memcg;

		nr_reclaimed = sc->nr_reclaimed;
		nr_scanned = sc->nr_scanned;

		memcg = mem_cgroup_iter(root, NULL, &reclaim);
		do {
			unsigned long lru_pages;
			unsigned long reclaimed;
			unsigned long scanned;

			if (mem_cgroup_low(root, memcg)) {
				if (!sc->memcg_low_reclaim) {
					sc->memcg_low_skipped = 1;
					continue;
				}
				mem_cgroup_event(memcg, MEMCG_LOW);
			}

			reclaimed = sc->nr_reclaimed;
			scanned = sc->nr_scanned;

			shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
			node_lru_pages += lru_pages;

			if (memcg)
				shrink_slab(sc->gfp_mask, pgdat->node_id,
					    memcg, sc->nr_scanned - scanned,
					    lru_pages);

			/* Record the group's reclaim efficiency */
			vmpressure(sc->gfp_mask, memcg, false,
				   sc->nr_scanned - scanned,
				   sc->nr_reclaimed - reclaimed);

			/*
			 * Direct reclaim and kswapd have to scan all memory
			 * cgroups to fulfill the overall scan target for the
			 * node.
			 *
			 * Limit reclaim, on the other hand, only cares about
			 * nr_to_reclaim pages to be reclaimed and it will
			 * retry with decreasing priority if one round over the
			 * whole hierarchy is not sufficient.
			 */
			if (!global_reclaim(sc) &&
					sc->nr_reclaimed >= sc->nr_to_reclaim) {
				mem_cgroup_iter_break(root, memcg);
				break;
			}
		} while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));

		/*
		 * Shrink the slab caches in the same proportion that
		 * the eligible LRU pages were scanned.
		 */
		if (global_reclaim(sc))
			shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
				    sc->nr_scanned - nr_scanned,
				    node_lru_pages);

		if (reclaim_state) {
			sc->nr_reclaimed += reclaim_state->reclaimed_slab;
			reclaim_state->reclaimed_slab = 0;
		}

		/* Record the subtree's reclaim efficiency */
		vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
			   sc->nr_scanned - nr_scanned,
			   sc->nr_reclaimed - nr_reclaimed);

		if (sc->nr_reclaimed - nr_reclaimed)
			reclaimable = true;

	} while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
					 sc->nr_scanned - nr_scanned, sc));

	/*
	 * Kswapd gives up on balancing particular nodes after too
	 * many failures to reclaim anything from them and goes to
	 * sleep. On reclaim progress, reset the failure counter. A
	 * successful direct reclaim run will revive a dormant kswapd.
	 */
	if (reclaimable)
		pgdat->kswapd_failures = 0;

	return reclaimable;
}

/*
 * Returns true if compaction should go ahead for a costly-order request, or
 * the allocation would already succeed without compaction. Return false if we
 * should reclaim first.
 */
static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
{
	unsigned long watermark;
	enum compact_result suitable;

	suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
	if (suitable == COMPACT_SUCCESS)
		/* Allocation should succeed already. Don't reclaim. */
		return true;
	if (suitable == COMPACT_SKIPPED)
		/* Compaction cannot yet proceed. Do reclaim. */
		return false;

	/*
	 * Compaction is already possible, but it takes time to run and there
	 * are potentially other callers using the pages just freed. So proceed
	 * with reclaim to make a buffer of free pages available to give
	 * compaction a reasonable chance of completing and allocating the page.
	 * Note that we won't actually reclaim the whole buffer in one attempt
	 * as the target watermark in should_continue_reclaim() is lower. But if
	 * we are already above the high+gap watermark, don't reclaim at all.
	 */
	watermark = high_wmark_pages(zone) + compact_gap(sc->order);

	return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
}

/*
 * This is the direct reclaim path, for page-allocating processes.  We only
 * try to reclaim pages from zones which will satisfy the caller's allocation
 * request.
 *
 * If a zone is deemed to be full of pinned pages then just give it a light
 * scan then give up on it.
 */
static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
{
	struct zoneref *z;
	struct zone *zone;
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
	gfp_t orig_mask;
	pg_data_t *last_pgdat = NULL;

	/*
	 * If the number of buffer_heads in the machine exceeds the maximum
	 * allowed level, force direct reclaim to scan the highmem zone as
	 * highmem pages could be pinning lowmem pages storing buffer_heads
	 */
	orig_mask = sc->gfp_mask;
	if (buffer_heads_over_limit) {
		sc->gfp_mask |= __GFP_HIGHMEM;
		sc->reclaim_idx = gfp_zone(sc->gfp_mask);
	}

	for_each_zone_zonelist_nodemask(zone, z, zonelist,
					sc->reclaim_idx, sc->nodemask) {
		/*
		 * Take care memory controller reclaiming has small influence
		 * to global LRU.
		 */
		if (global_reclaim(sc)) {
			if (!cpuset_zone_allowed(zone,
						 GFP_KERNEL | __GFP_HARDWALL))
				continue;

			/*
			 * If we already have plenty of memory free for
			 * compaction in this zone, don't free any more.
			 * Even though compaction is invoked for any
			 * non-zero order, only frequent costly order
			 * reclamation is disruptive enough to become a
			 * noticeable problem, like transparent huge
			 * page allocations.
			 */
			if (IS_ENABLED(CONFIG_COMPACTION) &&
			    sc->order > PAGE_ALLOC_COSTLY_ORDER &&
			    compaction_ready(zone, sc)) {
				sc->compaction_ready = true;
				continue;
			}

			/*
			 * Shrink each node in the zonelist once. If the
			 * zonelist is ordered by zone (not the default) then a
			 * node may be shrunk multiple times but in that case
			 * the user prefers lower zones being preserved.
			 */
			if (zone->zone_pgdat == last_pgdat)
				continue;

			/*
			 * This steals pages from memory cgroups over softlimit
			 * and returns the number of reclaimed pages and
			 * scanned pages. This works for global memory pressure
			 * and balancing, not for a memcg's limit.
			 */
			nr_soft_scanned = 0;
			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
						sc->order, sc->gfp_mask,
						&nr_soft_scanned);
			sc->nr_reclaimed += nr_soft_reclaimed;
			sc->nr_scanned += nr_soft_scanned;
			/* need some check for avoid more shrink_zone() */
		}

		/* See comment about same check for global reclaim above */
		if (zone->zone_pgdat == last_pgdat)
			continue;
		last_pgdat = zone->zone_pgdat;
		shrink_node(zone->zone_pgdat, sc);
	}

	/*
	 * Restore to original mask to avoid the impact on the caller if we
	 * promoted it to __GFP_HIGHMEM.
	 */
	sc->gfp_mask = orig_mask;
}

static void snapshot_refaults(struct mem_cgroup *root_memcg, pg_data_t *pgdat)
{
	struct mem_cgroup *memcg;

	memcg = mem_cgroup_iter(root_memcg, NULL, NULL);
	do {
		unsigned long refaults;
		struct lruvec *lruvec;

		if (memcg)
			refaults = memcg_page_state(memcg, WORKINGSET_ACTIVATE);
		else
			refaults = node_page_state(pgdat, WORKINGSET_ACTIVATE);

		lruvec = mem_cgroup_lruvec(pgdat, memcg);
		lruvec->refaults = refaults;
	} while ((memcg = mem_cgroup_iter(root_memcg, memcg, NULL)));
}

/*
 * This is the main entry point to direct page reclaim.
 *
 * If a full scan of the inactive list fails to free enough memory then we
 * are "out of memory" and something needs to be killed.
 *
 * If the caller is !__GFP_FS then the probability of a failure is reasonably
 * high - the zone may be full of dirty or under-writeback pages, which this
 * caller can't do much about.  We kick the writeback threads and take explicit
 * naps in the hope that some of these pages can be written.  But if the
 * allocating task holds filesystem locks which prevent writeout this might not
 * work, and the allocation attempt will fail.
 *
 * returns:	0, if no pages reclaimed
 * 		else, the number of pages reclaimed
 */
static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
					  struct scan_control *sc)
{
	int initial_priority = sc->priority;
	pg_data_t *last_pgdat;
	struct zoneref *z;
	struct zone *zone;
retry:
	delayacct_freepages_start();

	if (global_reclaim(sc))
		__count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);

	do {
		vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
				sc->priority);
		sc->nr_scanned = 0;
		shrink_zones(zonelist, sc);

		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
			break;

		if (sc->compaction_ready)
			break;

		/*
		 * If we're getting trouble reclaiming, start doing
		 * writepage even in laptop mode.
		 */
		if (sc->priority < DEF_PRIORITY - 2)
			sc->may_writepage = 1;
	} while (--sc->priority >= 0);

	last_pgdat = NULL;
	for_each_zone_zonelist_nodemask(zone, z, zonelist, sc->reclaim_idx,
					sc->nodemask) {
		if (zone->zone_pgdat == last_pgdat)
			continue;
		last_pgdat = zone->zone_pgdat;
		snapshot_refaults(sc->target_mem_cgroup, zone->zone_pgdat);
	}

	delayacct_freepages_end();

	if (sc->nr_reclaimed)
		return sc->nr_reclaimed;

	/* Aborted reclaim to try compaction? don't OOM, then */
	if (sc->compaction_ready)
		return 1;

	/* Untapped cgroup reserves?  Don't OOM, retry. */
	if (sc->memcg_low_skipped) {
		sc->priority = initial_priority;
		sc->memcg_low_reclaim = 1;
		sc->memcg_low_skipped = 0;
		goto retry;
	}

	return 0;
}

static bool allow_direct_reclaim(pg_data_t *pgdat)
{
	struct zone *zone;
	unsigned long pfmemalloc_reserve = 0;
	unsigned long free_pages = 0;
	int i;
	bool wmark_ok;

	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
		return true;

	for (i = 0; i <= ZONE_NORMAL; i++) {
		zone = &pgdat->node_zones[i];
		if (!managed_zone(zone))
			continue;

		if (!zone_reclaimable_pages(zone))
			continue;

		pfmemalloc_reserve += min_wmark_pages(zone);
		free_pages += zone_page_state(zone, NR_FREE_PAGES);
	}

	/* If there are no reserves (unexpected config) then do not throttle */
	if (!pfmemalloc_reserve)
		return true;

	wmark_ok = free_pages > pfmemalloc_reserve / 2;

	/* kswapd must be awake if processes are being throttled */
	if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
		pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
						(enum zone_type)ZONE_NORMAL);
		wake_up_interruptible(&pgdat->kswapd_wait);
	}

	return wmark_ok;
}

/*
 * Throttle direct reclaimers if backing storage is backed by the network
 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
 * depleted. kswapd will continue to make progress and wake the processes
 * when the low watermark is reached.
 *
 * Returns true if a fatal signal was delivered during throttling. If this
 * happens, the page allocator should not consider triggering the OOM killer.
 */
static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
					nodemask_t *nodemask)
{
	struct zoneref *z;
	struct zone *zone;
	pg_data_t *pgdat = NULL;

	/*
	 * Kernel threads should not be throttled as they may be indirectly
	 * responsible for cleaning pages necessary for reclaim to make forward
	 * progress. kjournald for example may enter direct reclaim while
	 * committing a transaction where throttling it could forcing other
	 * processes to block on log_wait_commit().
	 */
	if (current->flags & PF_KTHREAD)
		goto out;

	/*
	 * If a fatal signal is pending, this process should not throttle.
	 * It should return quickly so it can exit and free its memory
	 */
	if (fatal_signal_pending(current))
		goto out;

	/*
	 * Check if the pfmemalloc reserves are ok by finding the first node
	 * with a usable ZONE_NORMAL or lower zone. The expectation is that
	 * GFP_KERNEL will be required for allocating network buffers when
	 * swapping over the network so ZONE_HIGHMEM is unusable.
	 *
	 * Throttling is based on the first usable node and throttled processes
	 * wait on a queue until kswapd makes progress and wakes them. There
	 * is an affinity then between processes waking up and where reclaim
	 * progress has been made assuming the process wakes on the same node.
	 * More importantly, processes running on remote nodes will not compete
	 * for remote pfmemalloc reserves and processes on different nodes
	 * should make reasonable progress.
	 */
	for_each_zone_zonelist_nodemask(zone, z, zonelist,
					gfp_zone(gfp_mask), nodemask) {
		if (zone_idx(zone) > ZONE_NORMAL)
			continue;

		/* Throttle based on the first usable node */
		pgdat = zone->zone_pgdat;
		if (allow_direct_reclaim(pgdat))
			goto out;
		break;
	}

	/* If no zone was usable by the allocation flags then do not throttle */
	if (!pgdat)
		goto out;

	/* Account for the throttling */
	count_vm_event(PGSCAN_DIRECT_THROTTLE);

	/*
	 * If the caller cannot enter the filesystem, it's possible that it
	 * is due to the caller holding an FS lock or performing a journal
	 * transaction in the case of a filesystem like ext[3|4]. In this case,
	 * it is not safe to block on pfmemalloc_wait as kswapd could be
	 * blocked waiting on the same lock. Instead, throttle for up to a
	 * second before continuing.
	 */
	if (!(gfp_mask & __GFP_FS)) {
		wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
			allow_direct_reclaim(pgdat), HZ);

		goto check_pending;
	}

	/* Throttle until kswapd wakes the process */
	wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
		allow_direct_reclaim(pgdat));

check_pending:
	if (fatal_signal_pending(current))
		return true;

out:
	return false;
}

unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
				gfp_t gfp_mask, nodemask_t *nodemask)
{
	unsigned long nr_reclaimed;
	struct scan_control sc = {
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
		.gfp_mask = current_gfp_context(gfp_mask),
		.reclaim_idx = gfp_zone(gfp_mask),
		.order = order,
		.nodemask = nodemask,
		.priority = DEF_PRIORITY,
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
		.may_swap = 1,
	};

	/*
	 * Do not enter reclaim if fatal signal was delivered while throttled.
	 * 1 is returned so that the page allocator does not OOM kill at this
	 * point.
	 */
	if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
		return 1;

	trace_mm_vmscan_direct_reclaim_begin(order,
				sc.may_writepage,
				sc.gfp_mask,
				sc.reclaim_idx);

	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);

	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
}

#ifdef CONFIG_MEMCG

unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
						gfp_t gfp_mask, bool noswap,
						pg_data_t *pgdat,
						unsigned long *nr_scanned)
{
	struct scan_control sc = {
		.nr_to_reclaim = SWAP_CLUSTER_MAX,
		.target_mem_cgroup = memcg,
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
		.reclaim_idx = MAX_NR_ZONES - 1,
		.may_swap = !noswap,
	};
	unsigned long lru_pages;

	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);

	trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
						      sc.may_writepage,
						      sc.gfp_mask,
						      sc.reclaim_idx);

	/*
	 * NOTE: Although we can get the priority field, using it
	 * here is not a good idea, since it limits the pages we can scan.
	 * if we don't reclaim here, the shrink_node from balance_pgdat
	 * will pick up pages from other mem cgroup's as well. We hack
	 * the priority and make it zero.
	 */
	shrink_node_memcg(pgdat, memcg, &sc, &lru_pages);

	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);

	*nr_scanned = sc.nr_scanned;
	return sc.nr_reclaimed;
}

unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
					   unsigned long nr_pages,
					   gfp_t gfp_mask,
					   bool may_swap)
{
	struct zonelist *zonelist;
	unsigned long nr_reclaimed;
	int nid;
	unsigned int noreclaim_flag;
	struct scan_control sc = {
		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
		.gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) |
				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
		.reclaim_idx = MAX_NR_ZONES - 1,
		.target_mem_cgroup = memcg,
		.priority = DEF_PRIORITY,
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
		.may_swap = may_swap,
	};

	/*
	 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
	 * take care of from where we get pages. So the node where we start the
	 * scan does not need to be the current node.
	 */
	nid = mem_cgroup_select_victim_node(memcg);

	zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK];

	trace_mm_vmscan_memcg_reclaim_begin(0,
					    sc.may_writepage,
					    sc.gfp_mask,
					    sc.reclaim_idx);

	noreclaim_flag = memalloc_noreclaim_save();
	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
	memalloc_noreclaim_restore(noreclaim_flag);

	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);

	return nr_reclaimed;
}
#endif

static void age_active_anon(struct pglist_data *pgdat,
				struct scan_control *sc)
{
	struct mem_cgroup *memcg;

	if (!total_swap_pages)
		return;

	memcg = mem_cgroup_iter(NULL, NULL, NULL);
	do {
		struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);

		if (inactive_list_is_low(lruvec, false, memcg, sc, true))
			shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
					   sc, LRU_ACTIVE_ANON);

		memcg = mem_cgroup_iter(NULL, memcg, NULL);
	} while (memcg);
}

/*
 * Returns true if there is an eligible zone balanced for the request order
 * and classzone_idx
 */
static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
{
	int i;
	unsigned long mark = -1;
	struct zone *zone;

	for (i = 0; i <= classzone_idx; i++) {
		zone = pgdat->node_zones + i;

		if (!managed_zone(zone))
			continue;

		mark = high_wmark_pages(zone);
		if (zone_watermark_ok_safe(zone, order, mark, classzone_idx))
			return true;
	}

	/*
	 * If a node has no populated zone within classzone_idx, it does not
	 * need balancing by definition. This can happen if a zone-restricted
	 * allocation tries to wake a remote kswapd.
	 */
	if (mark == -1)
		return true;

	return false;
}

/* Clear pgdat state for congested, dirty or under writeback. */
static void clear_pgdat_congested(pg_data_t *pgdat)
{
	clear_bit(PGDAT_CONGESTED, &pgdat->flags);
	clear_bit(PGDAT_DIRTY, &pgdat->flags);
	clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
}

/*
 * Prepare kswapd for sleeping. This verifies that there are no processes
 * waiting in throttle_direct_reclaim() and that watermarks have been met.
 *
 * Returns true if kswapd is ready to sleep
 */
static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx)
{
	/*
	 * The throttled processes are normally woken up in balance_pgdat() as
	 * soon as allow_direct_reclaim() is true. But there is a potential
	 * race between when kswapd checks the watermarks and a process gets
	 * throttled. There is also a potential race if processes get
	 * throttled, kswapd wakes, a large process exits thereby balancing the
	 * zones, which causes kswapd to exit balance_pgdat() before reaching
	 * the wake up checks. If kswapd is going to sleep, no process should
	 * be sleeping on pfmemalloc_wait, so wake them now if necessary. If
	 * the wake up is premature, processes will wake kswapd and get
	 * throttled again. The difference from wake ups in balance_pgdat() is
	 * that here we are under prepare_to_wait().
	 */
	if (waitqueue_active(&pgdat->pfmemalloc_wait))
		wake_up_all(&pgdat->pfmemalloc_wait);

	/* Hopeless node, leave it to direct reclaim */
	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
		return true;

	if (pgdat_balanced(pgdat, order, classzone_idx)) {
		clear_pgdat_congested(pgdat);
		return true;
	}

	return false;
}

/*
 * kswapd shrinks a node of pages that are at or below the highest usable
 * zone that is currently unbalanced.
 *
 * Returns true if kswapd scanned at least the requested number of pages to
 * reclaim or if the lack of progress was due to pages under writeback.
 * This is used to determine if the scanning priority needs to be raised.
 */
static bool kswapd_shrink_node(pg_data_t *pgdat,
			       struct scan_control *sc)
{
	struct zone *zone;
	int z;

	/* Reclaim a number of pages proportional to the number of zones */
	sc->nr_to_reclaim = 0;
	for (z = 0; z <= sc->reclaim_idx; z++) {
		zone = pgdat->node_zones + z;
		if (!managed_zone(zone))
			continue;

		sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
	}

	/*
	 * Historically care was taken to put equal pressure on all zones but
	 * now pressure is applied based on node LRU order.
	 */
	shrink_node(pgdat, sc);

	/*
	 * Fragmentation may mean that the system cannot be rebalanced for
	 * high-order allocations. If twice the allocation size has been
	 * reclaimed then recheck watermarks only at order-0 to prevent
	 * excessive reclaim. Assume that a process requested a high-order
	 * can direct reclaim/compact.
	 */
	if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
		sc->order = 0;

	return sc->nr_scanned >= sc->nr_to_reclaim;
}

/*
 * For kswapd, balance_pgdat() will reclaim pages across a node from zones
 * that are eligible for use by the caller until at least one zone is
 * balanced.
 *
 * Returns the order kswapd finished reclaiming at.
 *
 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
 * found to have free_pages <= high_wmark_pages(zone), any page is that zone
 * or lower is eligible for reclaim until at least one usable zone is
 * balanced.
 */
static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
{
	int i;
	unsigned long nr_soft_reclaimed;
	unsigned long nr_soft_scanned;
	struct zone *zone;
	struct scan_control sc = {
		.gfp_mask = GFP_KERNEL,
		.order = order,
		.priority = DEF_PRIORITY,
		.may_writepage = !laptop_mode,
		.may_unmap = 1,
		.may_swap = 1,
	};
	count_vm_event(PAGEOUTRUN);

	do {
		unsigned long nr_reclaimed = sc.nr_reclaimed;
		bool raise_priority = true;

		sc.reclaim_idx = classzone_idx;

		/*
		 * If the number of buffer_heads exceeds the maximum allowed
		 * then consider reclaiming from all zones. This has a dual
		 * purpose -- on 64-bit systems it is expected that
		 * buffer_heads are stripped during active rotation. On 32-bit
		 * systems, highmem pages can pin lowmem memory and shrinking
		 * buffers can relieve lowmem pressure. Reclaim may still not
		 * go ahead if all eligible zones for the original allocation
		 * request are balanced to avoid excessive reclaim from kswapd.
		 */
		if (buffer_heads_over_limit) {
			for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
				zone = pgdat->node_zones + i;
				if (!managed_zone(zone))
					continue;

				sc.reclaim_idx = i;
				break;
			}
		}

		/*
		 * Only reclaim if there are no eligible zones. Note that
		 * sc.reclaim_idx is not used as buffer_heads_over_limit may
		 * have adjusted it.
		 */
		if (pgdat_balanced(pgdat, sc.order, classzone_idx))
			goto out;

		/*
		 * Do some background aging of the anon list, to give
		 * pages a chance to be referenced before reclaiming. All
		 * pages are rotated regardless of classzone as this is
		 * about consistent aging.
		 */
		age_active_anon(pgdat, &sc);

		/*
		 * If we're getting trouble reclaiming, start doing writepage
		 * even in laptop mode.
		 */
		if (sc.priority < DEF_PRIORITY - 2)
			sc.may_writepage = 1;

		/* Call soft limit reclaim before calling shrink_node. */
		sc.nr_scanned = 0;
		nr_soft_scanned = 0;
		nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
						sc.gfp_mask, &nr_soft_scanned);
		sc.nr_reclaimed += nr_soft_reclaimed;

		/*
		 * There should be no need to raise the scanning priority if
		 * enough pages are already being scanned that that high
		 * watermark would be met at 100% efficiency.
		 */
		if (kswapd_shrink_node(pgdat, &sc))
			raise_priority = false;

		/*
		 * If the low watermark is met there is no need for processes
		 * to be throttled on pfmemalloc_wait as they should not be
		 * able to safely make forward progress. Wake them
		 */
		if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
				allow_direct_reclaim(pgdat))
			wake_up_all(&pgdat->pfmemalloc_wait);

		/* Check if kswapd should be suspending */
		if (try_to_freeze() || kthread_should_stop())
			break;

		/*
		 * Raise priority if scanning rate is too low or there was no
		 * progress in reclaiming pages
		 */
		nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
		if (raise_priority || !nr_reclaimed)
			sc.priority--;
	} while (sc.priority >= 1);

	if (!sc.nr_reclaimed)
		pgdat->kswapd_failures++;

out:
	snapshot_refaults(NULL, pgdat);
	/*
	 * Return the order kswapd stopped reclaiming at as
	 * prepare_kswapd_sleep() takes it into account. If another caller
	 * entered the allocator slow path while kswapd was awake, order will
	 * remain at the higher level.
	 */
	return sc.order;
}

/*
 * pgdat->kswapd_classzone_idx is the highest zone index that a recent
 * allocation request woke kswapd for. When kswapd has not woken recently,
 * the value is MAX_NR_ZONES which is not a valid index. This compares a
 * given classzone and returns it or the highest classzone index kswapd
 * was recently woke for.
 */
static enum zone_type kswapd_classzone_idx(pg_data_t *pgdat,
					   enum zone_type classzone_idx)
{
	if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES)
		return classzone_idx;

	return max(pgdat->kswapd_classzone_idx, classzone_idx);
}

static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
				unsigned int classzone_idx)
{
	long remaining = 0;
	DEFINE_WAIT(wait);

	if (freezing(current) || kthread_should_stop())
		return;

	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);

	/*
	 * Try to sleep for a short interval. Note that kcompactd will only be
	 * woken if it is possible to sleep for a short interval. This is
	 * deliberate on the assumption that if reclaim cannot keep an
	 * eligible zone balanced that it's also unlikely that compaction will
	 * succeed.
	 */
	if (prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
		/*
		 * Compaction records what page blocks it recently failed to
		 * isolate pages from and skips them in the future scanning.
		 * When kswapd is going to sleep, it is reasonable to assume
		 * that pages and compaction may succeed so reset the cache.
		 */
		reset_isolation_suitable(pgdat);

		/*
		 * We have freed the memory, now we should compact it to make
		 * allocation of the requested order possible.
		 */
		wakeup_kcompactd(pgdat, alloc_order, classzone_idx);

		remaining = schedule_timeout(HZ/10);

		/*
		 * If woken prematurely then reset kswapd_classzone_idx and
		 * order. The values will either be from a wakeup request or
		 * the previous request that slept prematurely.
		 */
		if (remaining) {
			pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
			pgdat->kswapd_order = max(pgdat->kswapd_order, reclaim_order);
		}

		finish_wait(&pgdat->kswapd_wait, &wait);
		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
	}

	/*
	 * After a short sleep, check if it was a premature sleep. If not, then
	 * go fully to sleep until explicitly woken up.
	 */
	if (!remaining &&
	    prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
		trace_mm_vmscan_kswapd_sleep(pgdat->node_id);

		/*
		 * vmstat counters are not perfectly accurate and the estimated
		 * value for counters such as NR_FREE_PAGES can deviate from the
		 * true value by nr_online_cpus * threshold. To avoid the zone
		 * watermarks being breached while under pressure, we reduce the
		 * per-cpu vmstat threshold while kswapd is awake and restore
		 * them before going back to sleep.
		 */
		set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);

		if (!kthread_should_stop())
			schedule();

		set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
	} else {
		if (remaining)
			count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
		else
			count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
	}
	finish_wait(&pgdat->kswapd_wait, &wait);
}

/*
 * The background pageout daemon, started as a kernel thread
 * from the init process.
 *
 * This basically trickles out pages so that we have _some_
 * free memory available even if there is no other activity
 * that frees anything up. This is needed for things like routing
 * etc, where we otherwise might have all activity going on in
 * asynchronous contexts that cannot page things out.
 *
 * If there are applications that are active memory-allocators
 * (most normal use), this basically shouldn't matter.
 */
static int kswapd(void *p)
{
	unsigned int alloc_order, reclaim_order;
	unsigned int classzone_idx = MAX_NR_ZONES - 1;
	pg_data_t *pgdat = (pg_data_t*)p;
	struct task_struct *tsk = current;

	struct reclaim_state reclaim_state = {
		.reclaimed_slab = 0,
	};
	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);

	if (!cpumask_empty(cpumask))
		set_cpus_allowed_ptr(tsk, cpumask);
	current->reclaim_state = &reclaim_state;

	/*
	 * Tell the memory management that we're a "memory allocator",
	 * and that if we need more memory we should get access to it
	 * regardless (see "__alloc_pages()"). "kswapd" should
	 * never get caught in the normal page freeing logic.
	 *
	 * (Kswapd normally doesn't need memory anyway, but sometimes
	 * you need a small amount of memory in order to be able to
	 * page out something else, and this flag essentially protects
	 * us from recursively trying to free more memory as we're
	 * trying to free the first piece of memory in the first place).
	 */
	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
	set_freezable();

	pgdat->kswapd_order = 0;
	pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
	for ( ; ; ) {
		bool ret;

		alloc_order = reclaim_order = pgdat->kswapd_order;
		classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);

kswapd_try_sleep:
		kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
					classzone_idx);

		/* Read the new order and classzone_idx */
		alloc_order = reclaim_order = pgdat->kswapd_order;
		classzone_idx = kswapd_classzone_idx(pgdat, 0);
		pgdat->kswapd_order = 0;
		pgdat->kswapd_classzone_idx = MAX_NR_ZONES;

		ret = try_to_freeze();
		if (kthread_should_stop())
			break;

		/*
		 * We can speed up thawing tasks if we don't call balance_pgdat
		 * after returning from the refrigerator
		 */
		if (ret)
			continue;

		/*
		 * Reclaim begins at the requested order but if a high-order
		 * reclaim fails then kswapd falls back to reclaiming for
		 * order-0. If that happens, kswapd will consider sleeping
		 * for the order it finished reclaiming at (reclaim_order)
		 * but kcompactd is woken to compact for the original
		 * request (alloc_order).
		 */
		trace_mm_vmscan_kswapd_wake(pgdat->node_id, classzone_idx,
						alloc_order);
		fs_reclaim_acquire(GFP_KERNEL);
		reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
		fs_reclaim_release(GFP_KERNEL);
		if (reclaim_order < alloc_order)
			goto kswapd_try_sleep;
	}

	tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
	current->reclaim_state = NULL;

	return 0;
}

/*
 * A zone is low on free memory, so wake its kswapd task to service it.
 */
void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
{
	pg_data_t *pgdat;

	if (!managed_zone(zone))
		return;

	if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL))
		return;
	pgdat = zone->zone_pgdat;
	pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat,
							   classzone_idx);
	pgdat->kswapd_order = max(pgdat->kswapd_order, order);
	if (!waitqueue_active(&pgdat->kswapd_wait))
		return;

	/* Hopeless node, leave it to direct reclaim */
	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
		return;

	if (pgdat_balanced(pgdat, order, classzone_idx))
		return;

	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, classzone_idx, order);
	wake_up_interruptible(&pgdat->kswapd_wait);
}

#ifdef CONFIG_HIBERNATION
/*
 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
 * freed pages.
 *
 * Rather than trying to age LRUs the aim is to preserve the overall
 * LRU order by reclaiming preferentially
 * inactive > active > active referenced > active mapped
 */
unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
{
	struct reclaim_state reclaim_state;
	struct scan_control sc = {
		.nr_to_reclaim = nr_to_reclaim,
		.gfp_mask = GFP_HIGHUSER_MOVABLE,
		.reclaim_idx = MAX_NR_ZONES - 1,
		.priority = DEF_PRIORITY,
		.may_writepage = 1,
		.may_unmap = 1,
		.may_swap = 1,
		.hibernation_mode = 1,
	};
	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
	struct task_struct *p = current;
	unsigned long nr_reclaimed;
	unsigned int noreclaim_flag;

	noreclaim_flag = memalloc_noreclaim_save();
	fs_reclaim_acquire(sc.gfp_mask);
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;

	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);

	p->reclaim_state = NULL;
	fs_reclaim_release(sc.gfp_mask);
	memalloc_noreclaim_restore(noreclaim_flag);

	return nr_reclaimed;
}
#endif /* CONFIG_HIBERNATION */

/* It's optimal to keep kswapds on the same CPUs as their memory, but
   not required for correctness.  So if the last cpu in a node goes
   away, we get changed to run anywhere: as the first one comes back,
   restore their cpu bindings. */
static int kswapd_cpu_online(unsigned int cpu)
{
	int nid;

	for_each_node_state(nid, N_MEMORY) {
		pg_data_t *pgdat = NODE_DATA(nid);
		const struct cpumask *mask;

		mask = cpumask_of_node(pgdat->node_id);

		if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
			/* One of our CPUs online: restore mask */
			set_cpus_allowed_ptr(pgdat->kswapd, mask);
	}
	return 0;
}

/*
 * This kswapd start function will be called by init and node-hot-add.
 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
 */
int kswapd_run(int nid)
{
	pg_data_t *pgdat = NODE_DATA(nid);
	int ret = 0;

	if (pgdat->kswapd)
		return 0;

	pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
	if (IS_ERR(pgdat->kswapd)) {
		/* failure at boot is fatal */
		BUG_ON(system_state < SYSTEM_RUNNING);
		pr_err("Failed to start kswapd on node %d\n", nid);
		ret = PTR_ERR(pgdat->kswapd);
		pgdat->kswapd = NULL;
	}
	return ret;
}

/*
 * Called by memory hotplug when all memory in a node is offlined.  Caller must
 * hold mem_hotplug_begin/end().
 */
void kswapd_stop(int nid)
{
	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;

	if (kswapd) {
		kthread_stop(kswapd);
		NODE_DATA(nid)->kswapd = NULL;
	}
}

static int __init kswapd_init(void)
{
	int nid, ret;

	swap_setup();
	for_each_node_state(nid, N_MEMORY)
 		kswapd_run(nid);
	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
					"mm/vmscan:online", kswapd_cpu_online,
					NULL);
	WARN_ON(ret < 0);
	return 0;
}

module_init(kswapd_init)

#ifdef CONFIG_NUMA
/*
 * Node reclaim mode
 *
 * If non-zero call node_reclaim when the number of free pages falls below
 * the watermarks.
 */
int node_reclaim_mode __read_mostly;

#define RECLAIM_OFF 0
#define RECLAIM_ZONE (1<<0)	/* Run shrink_inactive_list on the zone */
#define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
#define RECLAIM_UNMAP (1<<2)	/* Unmap pages during reclaim */

/*
 * Priority for NODE_RECLAIM. This determines the fraction of pages
 * of a node considered for each zone_reclaim. 4 scans 1/16th of
 * a zone.
 */
#define NODE_RECLAIM_PRIORITY 4

/*
 * Percentage of pages in a zone that must be unmapped for node_reclaim to
 * occur.
 */
int sysctl_min_unmapped_ratio = 1;

/*
 * If the number of slab pages in a zone grows beyond this percentage then
 * slab reclaim needs to occur.
 */
int sysctl_min_slab_ratio = 5;

static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
{
	unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED);
	unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) +
		node_page_state(pgdat, NR_ACTIVE_FILE);

	/*
	 * It's possible for there to be more file mapped pages than
	 * accounted for by the pages on the file LRU lists because
	 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
	 */
	return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
}

/* Work out how many page cache pages we can reclaim in this reclaim_mode */
static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
{
	unsigned long nr_pagecache_reclaimable;
	unsigned long delta = 0;

	/*
	 * If RECLAIM_UNMAP is set, then all file pages are considered
	 * potentially reclaimable. Otherwise, we have to worry about
	 * pages like swapcache and node_unmapped_file_pages() provides
	 * a better estimate
	 */
	if (node_reclaim_mode & RECLAIM_UNMAP)
		nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
	else
		nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);

	/* If we can't clean pages, remove dirty pages from consideration */
	if (!(node_reclaim_mode & RECLAIM_WRITE))
		delta += node_page_state(pgdat, NR_FILE_DIRTY);

	/* Watch for any possible underflows due to delta */
	if (unlikely(delta > nr_pagecache_reclaimable))
		delta = nr_pagecache_reclaimable;

	return nr_pagecache_reclaimable - delta;
}

/*
 * Try to free up some pages from this node through reclaim.
 */
static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
{
	/* Minimum pages needed in order to stay on node */
	const unsigned long nr_pages = 1 << order;
	struct task_struct *p = current;
	struct reclaim_state reclaim_state;
	unsigned int noreclaim_flag;
	struct scan_control sc = {
		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
		.gfp_mask = current_gfp_context(gfp_mask),
		.order = order,
		.priority = NODE_RECLAIM_PRIORITY,
		.may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
		.may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
		.may_swap = 1,
		.reclaim_idx = gfp_zone(gfp_mask),
	};

	cond_resched();
	/*
	 * We need to be able to allocate from the reserves for RECLAIM_UNMAP
	 * and we also need to be able to write out pages for RECLAIM_WRITE
	 * and RECLAIM_UNMAP.
	 */
	noreclaim_flag = memalloc_noreclaim_save();
	p->flags |= PF_SWAPWRITE;
	fs_reclaim_acquire(sc.gfp_mask);
	reclaim_state.reclaimed_slab = 0;
	p->reclaim_state = &reclaim_state;

	if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
		/*
		 * Free memory by calling shrink zone with increasing
		 * priorities until we have enough memory freed.
		 */
		do {
			shrink_node(pgdat, &sc);
		} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
	}

	p->reclaim_state = NULL;
	fs_reclaim_release(gfp_mask);
	current->flags &= ~PF_SWAPWRITE;
	memalloc_noreclaim_restore(noreclaim_flag);
	return sc.nr_reclaimed >= nr_pages;
}

int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
{
	int ret;

	/*
	 * Node reclaim reclaims unmapped file backed pages and
	 * slab pages if we are over the defined limits.
	 *
	 * A small portion of unmapped file backed pages is needed for
	 * file I/O otherwise pages read by file I/O will be immediately
	 * thrown out if the node is overallocated. So we do not reclaim
	 * if less than a specified percentage of the node is used by
	 * unmapped file backed pages.
	 */
	if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
	    node_page_state(pgdat, NR_SLAB_RECLAIMABLE) <= pgdat->min_slab_pages)
		return NODE_RECLAIM_FULL;

	/*
	 * Do not scan if the allocation should not be delayed.
	 */
	if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
		return NODE_RECLAIM_NOSCAN;

	/*
	 * Only run node reclaim on the local node or on nodes that do not
	 * have associated processors. This will favor the local processor
	 * over remote processors and spread off node memory allocations
	 * as wide as possible.
	 */
	if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
		return NODE_RECLAIM_NOSCAN;

	if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
		return NODE_RECLAIM_NOSCAN;

	ret = __node_reclaim(pgdat, gfp_mask, order);
	clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);

	if (!ret)
		count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);

	return ret;
}
#endif

/*
 * page_evictable - test whether a page is evictable
 * @page: the page to test
 *
 * Test whether page is evictable--i.e., should be placed on active/inactive
 * lists vs unevictable list.
 *
 * Reasons page might not be evictable:
 * (1) page's mapping marked unevictable
 * (2) page is part of an mlocked VMA
 *
 */
int page_evictable(struct page *page)
{
	return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
}

#ifdef CONFIG_SHMEM
/**
 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
 * @pages:	array of pages to check
 * @nr_pages:	number of pages to check
 *
 * Checks pages for evictability and moves them to the appropriate lru list.
 *
 * This function is only used for SysV IPC SHM_UNLOCK.
 */
void check_move_unevictable_pages(struct page **pages, int nr_pages)
{
	struct lruvec *lruvec;
	struct pglist_data *pgdat = NULL;
	int pgscanned = 0;
	int pgrescued = 0;
	int i;

	for (i = 0; i < nr_pages; i++) {
		struct page *page = pages[i];
		struct pglist_data *pagepgdat = page_pgdat(page);

		pgscanned++;
		if (pagepgdat != pgdat) {
			if (pgdat)
				spin_unlock_irq(&pgdat->lru_lock);
			pgdat = pagepgdat;
			spin_lock_irq(&pgdat->lru_lock);
		}
		lruvec = mem_cgroup_page_lruvec(page, pgdat);

		if (!PageLRU(page) || !PageUnevictable(page))
			continue;

		if (page_evictable(page)) {
			enum lru_list lru = page_lru_base_type(page);

			VM_BUG_ON_PAGE(PageActive(page), page);
			ClearPageUnevictable(page);
			del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
			add_page_to_lru_list(page, lruvec, lru);
			pgrescued++;
		}
	}

	if (pgdat) {
		__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
		__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
		spin_unlock_irq(&pgdat->lru_lock);
	}
}
#endif /* CONFIG_SHMEM */
OpenPOWER on IntegriCloud