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

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Date:	Mon, 22 Sep 2014 18:14:20 +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 1/2] memcg: move memcg_{alloc,free}_cache_params to
 slab_common.c

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.

Thanks,
Vladimir
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