linux-kernel - Re: [PATCH v4] memcg: remove PCG_CACHE page

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Date:	Tue, 24 Jan 2012 15:54:11 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Michal Hocko <mhocko@...e.cz>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hughd@...gle.com>, Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH v4] memcg: remove PCG_CACHE page_cgroup flag

On Tue, Jan 24, 2012 at 12:16:44PM +0100, Johannes Weiner wrote:
> On Tue, Jan 24, 2012 at 12:16:36PM +0900, KAMEZAWA Hiroyuki wrote:
> > 
> > > Can we make this anon as well?
> > 
> > I'm sorry for long RTT. version 4 here.
> > ==
> > >From c40256561d6cdaee62be7ec34147e6079dc426f4 Mon Sep 17 00:00:00 2001
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > Date: Thu, 19 Jan 2012 17:09:41 +0900
> > Subject: [PATCH] memcg: remove PCG_CACHE
> > 
> > We record 'the page is cache' by PCG_CACHE bit to page_cgroup.
> > Here, "CACHE" means anonymous user pages (and SwapCache). This
> > doesn't include shmem.
> 
> !CACHE means anonymous/swapcache
> 
> > Consdering callers, at charge/uncharge, the caller should know
> > what  the page is and we don't need to record it by using 1bit
> > per page.
> > 
> > This patch removes PCG_CACHE bit and make callers of
> > mem_cgroup_charge_statistics() to specify what the page is.
> > 
> > Changelog since v3
> >  - renamed a variable 'rss' to 'anon'
> > 
> > Changelog since v2
> >  - removed 'not_rss', added 'anon'
> >  - changed a meaning of arguments to mem_cgroup_charge_statisitcs()
> >  - removed a patch to mem_cgroup_uncharge_cache
> >  - simplified comment.
> > 
> > Changelog since RFC.
> >  - rebased onto memcg-devel
> >  - rename 'file' to 'not_rss'
> >  - some cleanup and added comment.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> Acked-by: Johannes Weiner <hannes@...xchg.org>

Hold on, I think this patch is still not complete: end_migration()
directly uses __mem_cgroup_uncharge_common() with the FORCE charge
type.  This will uncharge all migrated anon pages as cache, when it
should decide based on PageAnon(used), which is the page where
->mapping is intact after migration.
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