linux-kernel - Re: [PATCH -mm 1/4] memcg, slab: do not schedule cache destruction when last page goes away

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Date:	Tue, 15 Apr 2014 14:32:17 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Vladimir Davydov <vdavydov@...allels.com>
cc:	Johannes Weiner <hannes@...xchg.org>, akpm@...ux-foundation.org,
	mhocko@...e.cz, glommer@...il.com, penberg@...nel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, devel@...nvz.org
Subject: Re: [PATCH -mm 1/4] memcg, slab: do not schedule cache destruction
 when last page goes away

On Tue, 15 Apr 2014, Vladimir Davydov wrote:

> > There is already logic in both slub and slab that does that on cache
> > close.
>
> Yeah, but here the question is when we should close caches left after memcg
> offline. Obviously we should do it after all objects of such a cache have
> gone, but when exactly? Do it immediately after the last kfree (have to count
> objects per cache then AFAIU) or may be check periodically (or on vmpressure)
> that the cache is empty by issuing kmem_cache_shrink and looking if
> memcg_params::nr_pages = 0?

Guess check once in a while if you have no other way to determine this. A
hook in kfree() would impact all users.

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