linux-kernel - Re: [PATCH v2 2/2] SLUB: Mark merged slab caches in /proc/slabinfo

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Message-ID: <4C8FE263.5070101@kernel.org>
Date:	Wed, 15 Sep 2010 00:00:19 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH v2 2/2] SLUB: Mark merged slab caches in /proc/slabinfo

  On 14.9.2010 23.56, David Rientjes wrote:
>> In my not-so-humble opinion, either the merging needs to go away
>> entirely, or the misleading output needs to be fixed.
> Cache merging may have been advertised as a bigger performance improvement
> than it actually is, and I don't do it in my own slab allocator for other
> reasons, but it does lead to more effective memory use by reducing slab
> fragmentation.  On one of my benchmarking servers, over 60% of caches are
> merged and /sys/kernel/slab/.../partial reports roughly the same percent
> of fewer total partial slabs over the system in comparison to
> slub_nomerge.
Last time I checked (and it's been a while), it did reduce _internal 
fragmentation_ for the naive "memory used after boot" scenario. I don't 
think I ever advertised it as a performance improvement. Dunno if 
somebody else did.

             Pekka
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