linux-kernel - Re: No, really, stop trying to delete slab until you've finished making slub perform as well

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Date:	Wed, 13 Aug 2008 08:10:04 -0500
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	KOSAKI Motohiro <m-kosaki@...es.dti.ne.jp>,
	Matthew Wilcox <matthew@....cx>,
	Pekka Enberg <penberg@...helsinki.fi>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Mel Gorman <mel@...net.ie>,
	andi@...stfloor.org, Rik van Riel <riel@...hat.com>
Subject: Re: No, really, stop trying to delete slab until you've finished
 making slub perform as well

KOSAKI Motohiro wrote:


> <SLUB>
> 
> % cat /proc/meminfo
>
> Slab:            1591680 kB
> SReclaimable:      12608 kB
> SUnreclaim:      1579072 kB

Unreclaimable grew very big.


> :t-0000128               28739     128     1.3G  20984/20984/8  512 0  99   0 *

Argh. Most slabs contain a single object. Probably due to the conflict resolution.


> kmalloc-192               4609     192    85.9M    1303/1303/8  341 0  99   1

And a similar but not so severe issue here.

The obvious fix is to avoid allocating another slab on conflict but how will
this impact performance?


Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2008-08-13 08:06:00.000000000 -0500
+++ linux-2.6/mm/slub.c	2008-08-13 08:07:59.000000000 -0500
@@ -1253,13 +1253,11 @@
 static inline int lock_and_freeze_slab(struct kmem_cache_node *n,
 							struct page *page)
 {
-	if (slab_trylock(page)) {
-		list_del(&page->lru);
-		n->nr_partial--;
-		__SetPageSlubFrozen(page);
-		return 1;
-	}
-	return 0;
+	slab_lock(page);
+	list_del(&page->lru);
+	n->nr_partial--;
+	__SetPageSlubFrozen(page);
+	return 1;
 }

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