Re: [PATCH] memcg: remove PCG_CACHE page_cgroup flag

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Michal Hocko <mhocko@suse.cz>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	"hannes@cmpxchg.org" <hannes@cmpxchg.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Hugh Dickins <hughd@google.com>, Ying Han <yinghan@google.com>
Subject: Re: [PATCH] memcg: remove PCG_CACHE page_cgroup flag
Date: Fri, 20 Jan 2012 08:56:44 +0900	[thread overview]
Message-ID: <20120120085644.60d14c17.kamezawa.hiroyu@jp.fujitsu.com> (raw)
In-Reply-To: <20120119134358.GC13932@tiehlicka.suse.cz>

On Thu, 19 Jan 2012 14:43:58 +0100
Michal Hocko <mhocko@suse.cz> wrote:

> On Thu 19-01-12 18:17:11, KAMEZAWA Hiroyuki wrote:
> > This patch is onto memcg-devel, can be applied to linux-next, too.
> 
> Just for record memcg-devel tree should _always_ be compatible with
> linux-next. It just contains patches which are memcg related to be more
> stable for memcg specific development.
> 
> > 
> > ==
> > From 529653c266b0682894d64e4797fcaf6a3c35db25 Mon Sep 17 00:00:00 2001
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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.
> 
> > 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 RFC.
> >  - rebased onto memcg-devel
> >  - rename 'file' to 'not_rss'
> 
> The name is confusing.
> 
> Other than that the patch looks reasonable. Minor comment bellow:
> 

will use 'anon'.

> >  - some cleanup and added comment.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > ---
> >  include/linux/page_cgroup.h |    8 +-----
> >  mm/memcontrol.c             |   55 ++++++++++++++++++++++++++----------------
> >  2 files changed, 35 insertions(+), 28 deletions(-)
> > 
> [...]
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index fb2dfc3..de7721d 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> [...]
> > @@ -2908,9 +2915,15 @@ void mem_cgroup_uncharge_page(struct page *page)
> >  
> >  void mem_cgroup_uncharge_cache_page(struct page *page)
> >  {
> > +	int ctype;
> > +
> >  	VM_BUG_ON(page_mapped(page));
> >  	VM_BUG_ON(page->mapping);
> > -	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE);
> > +	if (page_is_file_cache(page))
> > +		ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
> > +	else
> > +		ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
> > +	__mem_cgroup_uncharge_common(page, ctype);
> 
> OK, this makes sense but doesn't make any real difference now, so it is
> more a clean up, right?
> 

Yes. Johannes reuqested to remove this. I'll remove this in v3.

Thanks,
-Kame