74 lines
2.9 KiB
Diff
74 lines
2.9 KiB
Diff
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From owner-linux-mm@kvack.org Wed May 11 11:29:53 2011
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From: Mel Gorman <mgorman@suse.de>
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To: Andrew Morton <akpm@linux-foundation.org>
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Subject: [PATCH 2/3] mm: slub: Do not take expensive steps for SLUBs speculative high-order allocations
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Date: Wed, 11 May 2011 16:29:32 +0100
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Message-Id: <1305127773-10570-3-git-send-email-mgorman@suse.de>
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To avoid locking and per-cpu overhead, SLUB optimisically uses
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high-order allocations and falls back to lower allocations if they
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fail. However, by simply trying to allocate, the caller can enter
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compaction or reclaim - both of which are likely to cost more than the
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benefit of using high-order pages in SLUB. On a desktop system, two
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users report that the system is getting stalled with kswapd using large
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amounts of CPU.
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This patch prevents SLUB taking any expensive steps when trying to
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use high-order allocations. Instead, it is expected to fall back to
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smaller orders more aggressively. Testing from users was somewhat
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inconclusive on how much this helped but local tests showed it made
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a positive difference. It makes sense that falling back to order-0
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allocations is faster than entering compaction or direct reclaim.
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Signed-off-yet: Mel Gorman <mgorman@suse.de>
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---
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mm/page_alloc.c | 3 ++-
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mm/slub.c | 3 ++-
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2 files changed, 4 insertions(+), 2 deletions(-)
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diff --git a/mm/page_alloc.c b/mm/page_alloc.c
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index 9f8a97b..057f1e2 100644
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--- a/mm/page_alloc.c
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+++ b/mm/page_alloc.c
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@@ -1972,6 +1972,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
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{
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int alloc_flags = ALLOC_WMARK_MIN | ALLOC_CPUSET;
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const gfp_t wait = gfp_mask & __GFP_WAIT;
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+ const gfp_t can_wake_kswapd = !(gfp_mask & __GFP_NO_KSWAPD);
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/* __GFP_HIGH is assumed to be the same as ALLOC_HIGH to save a branch. */
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BUILD_BUG_ON(__GFP_HIGH != (__force gfp_t) ALLOC_HIGH);
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@@ -1984,7 +1985,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
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*/
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alloc_flags |= (__force int) (gfp_mask & __GFP_HIGH);
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- if (!wait) {
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+ if (!wait && can_wake_kswapd) {
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/*
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* Not worth trying to allocate harder for
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* __GFP_NOMEMALLOC even if it can't schedule.
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diff --git a/mm/slub.c b/mm/slub.c
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index 98c358d..1071723 100644
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--- a/mm/slub.c
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+++ b/mm/slub.c
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@@ -1170,7 +1170,8 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
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* Let the initial higher-order allocation fail under memory pressure
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* so we fall-back to the minimum order allocation.
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*/
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- alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) & ~__GFP_NOFAIL;
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+ alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) &
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+ ~(__GFP_NOFAIL | __GFP_WAIT);
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page = alloc_slab_page(alloc_gfp, node, oo);
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if (unlikely(!page)) {
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--
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1.7.3.4
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--
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