Messages in this thread Patch in this message | | | From | Joonsoo Kim <> | Subject | [PATCH] mm/slub: don't wait for high-order page allocation | Date | Fri, 31 Jul 2015 10:09:50 +0900 |
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Almost description is copied from commit fb05e7a89f50 ("net: don't wait for order-3 page allocation").
I saw excessive direct memory reclaim/compaction triggered by slub. This causes performance issues and add latency. Slub uses high-order allocation to reduce internal fragmentation and management overhead. But, direct memory reclaim/compaction has high overhead and the benefit of high-order allocation can't compensate the overhead of both work.
This patch makes auxiliary high-order allocation atomic. If there is no memory pressure and memory isn't fragmented, the alloction will still success, so we don't sacrifice high-order allocation's benefit here. If the atomic allocation fails, direct memory reclaim/compaction will not be triggered, allocation fallback to low-order immediately, hence the direct memory reclaim/compaction overhead is avoided. In the allocation failure case, kswapd is waken up and trying to make high-order freepages, so allocation could success next time.
Following is the test to measure effect of this patch.
System: QEMU, CPU 8, 512 MB Mem: 25% memory is allocated at random position to make fragmentation. Memory-hogger occupies 150 MB memory. Workload: hackbench -g 20 -l 1000
Average result by 10 runs (Base va Patched)
elapsed_time(s): 4.3468 vs 2.9838 compact_stall: 461.7 vs 73.6 pgmigrate_success: 28315.9 vs 7256.1
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> --- mm/slub.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/mm/slub.c b/mm/slub.c index 257283f..2d02a36 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1364,6 +1364,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node) * so we fall-back to the minimum order allocation. */ alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL; + if ((alloc_gfp & __GFP_WAIT) && oo_order(oo) > oo_order(s->min)) + alloc_gfp = alloc_gfp & ~__GFP_WAIT; page = alloc_slab_page(s, alloc_gfp, node, oo); if (unlikely(!page)) { -- 1.9.1
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