linux-kernel - Re: [PATCH 4/8] memcg, mm: move mem_cgroup_select_victim

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Message-ID: <20150709120835.GF13872@dhcp22.suse.cz>
Date:	Thu, 9 Jul 2015 14:08:35 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Greg Thelen <gthelen@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/8] memcg, mm: move mem_cgroup_select_victim_node into
 vmscan

On Wed 08-07-15 19:01:59, Vladimir Davydov wrote:
> On Wed, Jul 08, 2015 at 02:27:48PM +0200, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@...e.cz>
> > 
> > We currently have only one caller of mem_cgroup_select_victim_node which
> > is sitting in mm/vmscan.c and which is already wrapped by CONFIG_MEMCG
> > ifdef. Now that we have struct mem_cgroup visible outside of
> > mm/memcontrol.c we can move the function and its dependencies there.
> > This even shrinks the code size by few bytes:
> > 
> >    text    data     bss     dec     hex filename
> >  478509   65806   26384  570699   8b54b mm/built-in.o.before
> >  478445   65806   26384  570635   8b50b mm/built-in.o.after
> > 
> > Signed-off-by: Michal Hocko <mhocko@...e.cz>
> 
> I dislike this patch, because I don't see any reason why logic specific
> to per memcg reclaim should live in the file representing the global
> reclaim path.

Well the idea was that mem_cgroup_select_victim_node is specific to
try_to_free_mem_cgroup_pages. It is basically a split up of otherwise
large function for readability. Same applies to
mem_cgroup_may_update_nodemask. Having that code together makes some
sense to me.

On the other hand I do agree that at least
test_mem_cgroup_node_reclaimable is generally reusable and so it
shouldn't be in vmscan. I can move it back to memcontrol but that leaves
the generated code much worse.

Fair enough then, I will drop this patch.
-- 
Michal Hocko
SUSE Labs
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