linux-kernel - Re: [PATCH -mm 8/8] slab: reap dead memcg caches aggressively

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Message-ID: <20140603082124.GB6013@esperanza>
Date:	Tue, 3 Jun 2014 12:21:26 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Joonsoo Kim <js1304@...il.com>
CC:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH -mm 8/8] slab: reap dead memcg caches aggressively

On Mon, Jun 02, 2014 at 11:01:55PM +0900, Joonsoo Kim wrote:
> 2014-06-02 21:10 GMT+09:00 Vladimir Davydov <vdavydov@...allels.com>:
> > On Mon, Jun 02, 2014 at 01:41:55PM +0900, Joonsoo Kim wrote:
> >> According to my code reading, slabs_to_free() doesn't return number of
> >> free slabs. This bug is introduced by 0fa8103b. I think that it is
> >> better to fix it before applyting this patch. Otherwise, use n->free_objects
> >> instead of slabs_tofree() to achieve your purpose correctly.
> >
> > Hmm, I don't think slab_tofree() computes the number of free slabs
> > wrong. If we have N free objects, there may be
> > DIV_ROUND_UP(N,objs_per_slab) empty slabs at max, and that's exactly
> > what slab_tofree() does, no?
> 
[...]
> BTW, we don't need DIV_ROUND_UP. I think that just N / objs_per_slab is
> sufficient to get number of empty slabs at max. Am I missing too?

Yeah, you're right - DIV_ROUND_UP is obviously redundant, DIV would be
enough. Not a bug though.

Thanks.
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