linux-kernel - Re: [PATCH 1/2] memcg: move memcg_{alloc,free}_cache_params to slab

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Message-ID: <20140922145115.GI336@dhcp22.suse.cz>
Date:	Mon, 22 Sep 2014 16:51:15 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Vladimir Davydov <vdavydov@...allels.com>
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 1/2] memcg: move memcg_{alloc,free}_cache_params to
 slab_common.c

On Mon 22-09-14 18:14:20, Vladimir Davydov wrote:
> On Mon, Sep 22, 2014 at 03:52:45PM +0200, Michal Hocko wrote:
> > On Thu 18-09-14 19:50:19, Vladimir Davydov wrote:
> > > The only reason why they live in memcontrol.c is that we get/put css
> > > reference to the owner memory cgroup in them. However, we can do that in
> > > memcg_{un,}register_cache.
> > > 
> > > So let's move them to slab_common.c and make them static.
> > 
> > Why is it better?
> 
> First, I think that the less public interface functions we have in
> memcontrol.h the better. Since the functions I move don't depend on
> memcontrol, I think it's worth making them private to slab, especially
> taking into account that the arrays are defined on the slab's side too.
> 
> Second, the way how per-memcg arrays are updated looks rather awkward:
> it proceeds from memcontrol.c (__memcg_activate_kmem) to slab_common.c
> (memcg_update_all_caches) and back to memcontrol.c again
> (memcg_update_array_size). In the next patch I move the function
> relocating the arrays (memcg_update_array_size) to slab_common.c and
> therefore get rid this circular call path. I think we should have the
> cache allocation stuff in the same place where we have relocation,
> because it's easier to follow the code then. So I move arrays alloc/free
> functions to slab_common.c too.
> 
> The third point isn't obvious. In the "Per memcg slab shrinkers" patch
> set, which I sent recently, I have to update per-memcg list_lrus arrays
> too. And it's much easier and cleaner to do it in list_lru.c rather than
> in memcontrol.c. The current patchset makes cache arrays allocation path
> conform that of the upcoming list_lru.

Exactly what I would love to have in the changelog...

Thanks!
-- 
Michal Hocko
SUSE Labs
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