linux-kernel - Re: [PATCH -mm v2 1/3] slub: never fail to shrink cache

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Message-ID: <20150129161739.GE11463@esperanza>
Date:	Thu, 29 Jan 2015 19:17:39 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm v2 1/3] slub: never fail to shrink cache

On Thu, Jan 29, 2015 at 09:55:56AM -0600, Christoph Lameter wrote:
> On Thu, 29 Jan 2015, Vladimir Davydov wrote:
> 
> > Come to think of it, do we really need to optimize slab placement in
> > kmem_cache_shrink? None of its users except shrink_store expects it -
> > they just want to purge the cache before destruction, that's it. May be,
> > we'd better move slab placement optimization to a separate SLUB's
> > private function that would be called only by shrink_store, where we can
> > put up with kmalloc failures? Christoph, what do you think?
> 
> The slabinfo tool invokes kmem_cache_shrink to optimize placement.
> 
> Run
> 
> 	slabinfo -s
> 
> which can then be used to reduce the fragmentation.

Yeah, but the tool just writes 1 to /sys/kernel/slab/cache/shrink, i.e.
invokes shrink_store(), and I don't propose to remove slab placement
optimization from there. What I propose is to move slab placement
optimization from kmem_cache_shrink() to shrink_store(), because other
users of kmem_cache_shrink() don't seem to need it at all - they just
want to release empty slabs. Such a change wouldn't affect the behavior
of `slabinfo -s` at all.

Thanks,
Vladimir
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