From 04f05909e0fde36ba481ad4c850b666ebef1ac55 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Tue, 8 Sep 2015 15:04:30 -0700 Subject: zsmalloc: introduce zs_can_compact() function This function checks if class compaction will free any pages. Rephrasing -- do we have enough unused objects to form at least one ZS_EMPTY page and free it. It aborts compaction if class compaction will not result in any (further) savings. EXAMPLE (this debug output is not part of this patch set): - class size - number of allocated objects - number of used objects - max objects per zspage - pages per zspage - estimated number of pages that will be freed [..] class-512 objs:544 inuse:540 maxobj-per-zspage:8 pages-per-zspage:1 zspages-to-free:0 ... class-512 compaction is useless. break class-496 objs:660 inuse:570 maxobj-per-zspage:33 pages-per-zspage:4 zspages-to-free:2 class-496 objs:627 inuse:570 maxobj-per-zspage:33 pages-per-zspage:4 zspages-to-free:1 class-496 objs:594 inuse:570 maxobj-per-zspage:33 pages-per-zspage:4 zspages-to-free:0 ... class-496 compaction is useless. break class-448 objs:657 inuse:617 maxobj-per-zspage:9 pages-per-zspage:1 zspages-to-free:4 class-448 objs:648 inuse:617 maxobj-per-zspage:9 pages-per-zspage:1 zspages-to-free:3 class-448 objs:639 inuse:617 maxobj-per-zspage:9 pages-per-zspage:1 zspages-to-free:2 class-448 objs:630 inuse:617 maxobj-per-zspage:9 pages-per-zspage:1 zspages-to-free:1 class-448 objs:621 inuse:617 maxobj-per-zspage:9 pages-per-zspage:1 zspages-to-free:0 ... class-448 compaction is useless. break class-432 objs:728 inuse:685 maxobj-per-zspage:28 pages-per-zspage:3 zspages-to-free:1 class-432 objs:700 inuse:685 maxobj-per-zspage:28 pages-per-zspage:3 zspages-to-free:0 ... class-432 compaction is useless. break class-416 objs:819 inuse:705 maxobj-per-zspage:39 pages-per-zspage:4 zspages-to-free:2 class-416 objs:780 inuse:705 maxobj-per-zspage:39 pages-per-zspage:4 zspages-to-free:1 class-416 objs:741 inuse:705 maxobj-per-zspage:39 pages-per-zspage:4 zspages-to-free:0 ... class-416 compaction is useless. break class-400 objs:690 inuse:674 maxobj-per-zspage:10 pages-per-zspage:1 zspages-to-free:1 class-400 objs:680 inuse:674 maxobj-per-zspage:10 pages-per-zspage:1 zspages-to-free:0 ... class-400 compaction is useless. break class-384 objs:736 inuse:709 maxobj-per-zspage:32 pages-per-zspage:3 zspages-to-free:0 ... class-384 compaction is useless. break [..] Every "compaction is useless" indicates that we saved CPU cycles. class-512 has 544 object allocated 540 objects used 8 objects per-page Even if we have a ALMOST_EMPTY zspage, we still don't have enough room to migrate all of its objects and free this zspage; so compaction will not make a lot of sense, it's better to just leave it as is. Signed-off-by: Sergey Senozhatsky Acked-by: Minchan Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/zsmalloc.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) (limited to 'mm') diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 1227f8323e93..4b39e5eaf34f 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1676,6 +1676,29 @@ static struct page *isolate_source_page(struct size_class *class) return page; } +/* + * + * Based on the number of unused allocated objects calculate + * and return the number of pages that we can free. + * + * Should be called under class->lock. + */ +static unsigned long zs_can_compact(struct size_class *class) +{ + unsigned long obj_wasted; + + if (!zs_stat_get(class, CLASS_ALMOST_EMPTY)) + return 0; + + obj_wasted = zs_stat_get(class, OBJ_ALLOCATED) - + zs_stat_get(class, OBJ_USED); + + obj_wasted /= get_maxobj_per_zspage(class->size, + class->pages_per_zspage); + + return obj_wasted * get_pages_per_zspage(class->size); +} + static unsigned long __zs_compact(struct zs_pool *pool, struct size_class *class) { @@ -1689,6 +1712,9 @@ static unsigned long __zs_compact(struct zs_pool *pool, BUG_ON(!is_first_page(src_page)); + if (!zs_can_compact(class)) + break; + cc.index = 0; cc.s_page = src_page; -- cgit v1.2.1