From 45eb00cd3a034b8448f52fd9074e9b2b11d857c1 Mon Sep 17 00:00:00 2001 From: Joonsoo Kim Date: Fri, 4 Sep 2015 15:45:54 -0700 Subject: [PATCH] mm/slub: don't wait for high-order page allocation Description is almost 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 Cc: Christoph Lameter Cc: Pekka Enberg Acked-by: David Rientjes Cc: Shaohua Li Cc: Vlastimil Babka Cc: Michal Hocko Cc: Eric Dumazet Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slub.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/slub.c b/mm/slub.c index 7e9e508263fb..084184e706c6 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1362,6 +1362,8 @@ 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_NOMEMALLOC) & ~__GFP_WAIT; page = alloc_slab_page(s, alloc_gfp, node, oo); if (unlikely(!page)) { -- 2.20.1