linux-kernel - Re: [RFC][PATCH 4/7][memcg] memcg use ID in page

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Message-Id: <20100728114402.571b8ec6.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 28 Jul 2010 11:44:02 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	gthelen@...gle.com, m-ikeda@...jp.nec.com,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 4/7][memcg] memcg use ID in page_cgroup

On Tue, 27 Jul 2010 22:39:04 -0400
Vivek Goyal <vgoyal@...hat.com> wrote:

> On Tue, Jul 27, 2010 at 04:56:29PM +0900, KAMEZAWA Hiroyuki wrote:
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > 
> > Now, addresses of memory cgroup can be calculated by their ID without complex.
> > This patch relplaces pc->mem_cgroup from a pointer to a unsigned short.
> > On 64bit architecture, this offers us more 6bytes room per page_cgroup.
> > Use 2bytes for blkio-cgroup's page tracking. More 4bytes will be used for
> > some light-weight concurrent access.
> > 
> > We may able to move this id onto flags field but ...go step by step.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > ---
> >  include/linux/page_cgroup.h |    3 ++-
> >  mm/memcontrol.c             |   40 +++++++++++++++++++++++++---------------
> >  mm/page_cgroup.c            |    2 +-
> >  3 files changed, 28 insertions(+), 17 deletions(-)
> > 
> > Index: mmotm-0719/include/linux/page_cgroup.h
> > ===================================================================
> > --- mmotm-0719.orig/include/linux/page_cgroup.h
> > +++ mmotm-0719/include/linux/page_cgroup.h
> > @@ -12,7 +12,8 @@
> >   */
> >  struct page_cgroup {
> >  	unsigned long flags;
> > -	struct mem_cgroup *mem_cgroup;
> > +	unsigned short mem_cgroup;	/* ID of assigned memory cgroup */
> > +	unsigned short blk_cgroup;	/* Not Used..but will be. */
> 
> So later I shall have to use virtually indexed arrays in blkio controller?
> Or you are just using virtually indexed arrays for lookup speed and
> I can continue to use css_lookup() and not worry about using virtually
> indexed arrays.
> 
yes. you can use css_lookup() even if it's slow.

> So the idea is that when a page is allocated, also store the blk_group
> id and once that page is submitted for writeback, we should be able
> to associate it to right blkio group?
> 
blk_cgroup id can be attached whenever you wants. please overwrite 
page_cgroup->blk_cgroup when it's necessary.
Did you read Ikeda's patch ? I myself doesn't have patches at this point. 
This is just for make a room for recording blkio-ID, which was requested
for a year.

Hmm, but page-allocation-time doesn't sound very good for me.

Thanks.
-Kame

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