linux-kernel - Re: [PATCH -mm v2 8/8] slab: make dead memcg caches discard free slabs immediately

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Message-ID: <20140611081139.GA28258@js1304-P5Q-DELUXE>
Date:	Wed, 11 Jun 2014 17:11:39 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Christoph Lameter <cl@...two.org>, akpm@...ux-foundation.org,
	rientjes@...gle.com, penberg@...nel.org, hannes@...xchg.org,
	mhocko@...e.cz, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -mm v2 8/8] slab: make dead memcg caches discard free
 slabs immediately

On Tue, Jun 10, 2014 at 07:18:34PM +0400, Vladimir Davydov wrote:
> On Tue, Jun 10, 2014 at 09:26:19AM -0500, Christoph Lameter wrote:
> > On Tue, 10 Jun 2014, Vladimir Davydov wrote:
> > 
> > > Frankly, I incline to shrinking dead SLAB caches periodically from
> > > cache_reap too, because it looks neater and less intrusive to me. Also
> > > it has zero performance impact, which is nice.
> > >
> > > However, Christoph proposed to disable per cpu arrays for dead caches,
> > > similarly to SLUB, and I decided to give it a try, just to see the end
> > > code we'd have with it.
> > >
> > > I'm still not quite sure which way we should choose though...
> > 
> > Which one is cleaner?
> 
> To shrink dead caches aggressively, we only need to modify cache_reap
> (see https://lkml.org/lkml/2014/5/30/271).
> 
> To zap object arrays for dead caches (this is what this patch does), we
> have to:
>  - set array_cache->limit to 0 for each per cpu, shared, and alien array
>    caches on kmem_cache_shrink;
>  - make cpu/node hotplug paths init new array cache sizes to 0;
>  - make free paths (__cache_free, cache_free_alien) handle zero array
>    cache size properly, because currently they doesn't.
> 
> So IMO the first one (reaping dead caches periodically) requires less
> modifications and therefore is cleaner.

Yeah, I also like the first one.

Thanks.
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