linux-kernel - Re: Race condition between putback_lru_page and mem_cgroup_move

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Message-Id: <20080805200556.A891.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Tue, 05 Aug 2008 20:19:56 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	kosaki.motohiro@...fujitsu.com,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	MinChan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm <linux-mm@...ck.org>, Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Race condition between putback_lru_page and mem_cgroup_move_list

> In general yes, but in practice no. We have different paths through which a page
> can be reclaimed. Consider the following
> 
> 1. What happens if a global reclaim is in progress at the same time as memory
> cgroup reclaim and they are both looking at the same page?
> 2. In the shared reclaim infrastructure, we move pages and update statistics for
> pages belonging to a particular zone in a particular cgroup.

hehe, you said mem_cgroup_per_zone::lru_lock is unnecessary lock.

Also, we can two approach

  1. the pages are allowed to exist in different zone of memcg zone and 
     global zone.
     and recover later (by mem_cgroup_isolate_pages).
     here is current implementation.
  2. the pages aren't allowed to exist in different zone of memcg zone and 
     global zone.
     (you said its mail)

if we select 2, I hope mem_cgroup_move_lists is called by ____pagevec_lru_add
and add_page_to_unevictable_list.
then, page's global lru transition become memcg lru transition automatically.
it increase source code readability.




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