linux-kernel - Re: [patch 8/8] mm: make per-memcg lru lists exclusive

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Date:	Wed, 8 Jun 2011 17:04:47 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Ying Han <yinghan@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 8/8] mm: make per-memcg lru lists exclusive

On Thu 02-06-11 19:57:02, Johannes Weiner wrote:
> On Fri, Jun 03, 2011 at 12:54:39AM +0900, Hiroyuki Kamezawa wrote:
> > 2011/6/2 Johannes Weiner <hannes@...xchg.org>:
> > > On Thu, Jun 02, 2011 at 10:16:59PM +0900, Hiroyuki Kamezawa wrote:
[...]
> 
> > But it may put a page onto wrong memcgs if we do link a page to
> > another page's page->lru
> > because 2 pages may be in different cgroup each other.
> 
> Yes, I noticed that.  If it splits a huge page, it does not just add
> the tailpages to the lru head, but it links them next to the head
> page.
> 
> But I don't see how those pages could ever be in different memcgs?
> pages with page->mapping pointing to the same anon_vma are always in
> the same memcg, AFAIU.

Process can be moved to other memcg and without move_charge_at_immigrate
all previously faulted pages stay in the original group while all new
(not faulted yet) get into the new group while mapping doesn't change.
I guess this might happen with thp tailpages as well. But I do not think
this is a problem. The original group already got charged for the huge
page so we can keep all tail pages in it.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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