linux-ext4 - [PATCH 2/4] mm: slub: Do not wake kswapd for SLUBs speculative high-order allocations

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Date:	Fri, 13 May 2011 15:03:22 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Colin King <colin.king@...onical.com>,
	Raghavendra D Prabhu <raghu.prabhu13@...il.com>,
	Jan Kara <jack@...e.cz>, Chris Mason <chris.mason@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>
Subject: [PATCH 2/4] mm: slub: Do not wake kswapd for SLUBs speculative high-order allocations

To avoid locking and per-cpu overhead, SLUB optimisically uses
high-order allocations and falls back to lower allocations if they
fail.  However, by simply trying to allocate, kswapd is woken up to
start reclaiming at that order. On a desktop system, two users report
that the system is getting locked up with kswapd using large amounts
of CPU.  Using SLAB instead of SLUB made this problem go away.

This patch prevents kswapd being woken up for high-order allocations.
Testing indicated that with this patch applied, the system was much
harder to hang and even when it did, it eventually recovered.

Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 mm/slub.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 9d2e5e4..98c358d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1170,7 +1170,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
 	 * Let the initial higher-order allocation fail under memory pressure
 	 * so we fall-back to the minimum order allocation.
 	 */
-	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL;
+	alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY | __GFP_NO_KSWAPD) & ~__GFP_NOFAIL;
 
 	page = alloc_slab_page(alloc_gfp, node, oo);
 	if (unlikely(!page)) {
-- 
1.7.3.4

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