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-rw-r--r--mm/page_alloc.c20
1 files changed, 19 insertions, 1 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e2f26991fff1..fe753ecf2aa5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2681,6 +2681,7 @@ static void __meminit zone_init_free_lists(struct zone *zone)
static int zone_batchsize(struct zone *zone)
{
+#ifdef CONFIG_MMU
int batch;
/*
@@ -2706,9 +2707,26 @@ static int zone_batchsize(struct zone *zone)
* of pages of one half of the possible page colors
* and the other with pages of the other colors.
*/
- batch = (1 << (fls(batch + batch/2)-1)) - 1;
+ batch = rounddown_pow_of_two(batch + batch/2) - 1;
return batch;
+
+#else
+ /* The deferral and batching of frees should be suppressed under NOMMU
+ * conditions.
+ *
+ * The problem is that NOMMU needs to be able to allocate large chunks
+ * of contiguous memory as there's no hardware page translation to
+ * assemble apparent contiguous memory from discontiguous pages.
+ *
+ * Queueing large contiguous runs of pages for batching, however,
+ * causes the pages to actually be freed in smaller chunks. As there
+ * can be a significant delay between the individual batches being
+ * recycled, this leads to the once large chunks of space being
+ * fragmented and becoming unavailable for high-order allocations.
+ */
+ return 0;
+#endif
}
static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
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