linux-kernel - Re: Free memory never fully used, swapping

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Date:	Thu, 25 Nov 2010 19:18:49 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Simon Kirby <sim@...tway.ca>
Cc:	kosaki.motohiro@...fujitsu.com, Shaohua Li <shaohua.li@...el.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: Free memory never fully used, swapping

> There are actually a few problems here.  I think they are worth looking
> at them separately, unless "don't use order 3 allocations" is a valid
> statement, in which case we should fix slub.
> 
> The funny thing here is that slub.c's allocate_slab() calls alloc_pages()
> with flags | __GFP_NOWARN | __GFP_NORETRY, and intentionally tries a
> lower order allocation automatically if it fails.  This is why there is
> no allocation failure warning when this happens.  However, it is too late
> -- kswapd is woken and it ties to bring order 3 up to the watermark. 
> If we hacked __alloc_pages_slowpath() to not wake kswapd when
> __GFP_NOWARN is set, we would never see this problem and the slub
> optimization might still mostly work.  Either way, we should "fix" slub
> or "fix" order-3 allocations, so that other people who are using slub
> don't hit the same problem.

This?




Subject: [PATCH] slub: use no __GFP_WAIT instead __GFP_NORETRY

---
 mm/slub.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 8c66aef..0c77399 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1134,7 +1134,7 @@ 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_NOFAIL | __GFP_WAIT);
 
 	page = alloc_slab_page(alloc_gfp, node, oo);
 	if (unlikely(!page)) {
-- 
1.6.5.2




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