linux-kernel - Re: [PATCH 2/2] memcg: move memcg_update_cache_size to slab

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Message-ID: <20140922142035.GE18526@esperanza>
Date:	Mon, 22 Sep 2014 18:20:35 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 2/2] memcg: move memcg_update_cache_size to slab_common.c

On Mon, Sep 22, 2014 at 04:07:34PM +0200, Michal Hocko wrote:
> On Thu 18-09-14 19:50:20, Vladimir Davydov wrote:
> > The only reason why this function lives in memcontrol.c is that it
> > depends on memcg_caches_array_size. However, we can pass the new array
> > size immediately to it instead of new_id+1 so that it will be free of
> > any memcontrol.c dependencies.
> > 
> > So let's move this function to slab_common.c and make it static.
> 
> Why?

Jumping from memcontrol.c to slab_common.c and then back to memcontrol.c
while updating per-memcg caches looks ugly IMO. We can do the update on
the slab's side.

> besides that the patch does more code reshuffling which should be
> documented. I have got lost a bit to be honest.

It just makes it sane :-) Currently we walk over all slab caches each
time new kmemcg is created even if memcg_limited_groups_array_size
doesn't grow and we've actually nothing to do. So it moves cache id
allocation stuff to a separate function (memcg_alloc_cache_id) and
places the check there so that memcg_update_all_caches is only called
when it's really necessary.

I'm sorry if it confuses you. I thought the patch isn't big and rather
easy to understand :-/ Next time will split better.

Thanks,
Vladimir
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