linux-kernel - Re: [PATCH 9/12] memcg allocate all page

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Message-ID: <48E311A8.3000802@linux.vnet.ibm.com>
Date:	Wed, 01 Oct 2008 11:29:04 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"xemul@...nvz.org" <xemul@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Hansen <haveblue@...ibm.com>, ryov@...inux.co.jp
Subject: Re: [PATCH 9/12] memcg allocate all page_cgroup at boot

KAMEZAWA Hiroyuki wrote:
> On Wed, 1 Oct 2008 14:07:48 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
>>> Can we make this patch indepedent of the flags changes and push it in ASAP.
>>>
>> Need much work....Hmm..rewrite all again ? 
>>
> 
> BTW, do you have good idea to modify flag bit without affecting LOCK bit on
> page_cgroup->flags ?
> 
> At least, we'll have to set ACTIVE/INACTIVE/UNEVICTABLE flags dynamically.
> take lock_page_cgroup() always ?

In the past patches, I've used lock_page_cgroup(). In some cases like
initialization at boot time, I've ignored taking the lock, since I know no-one
is accessing them yet.

> __mem_cgroup_move_lists() will have some amount of changes. And we should
> check dead lock again.

__mem_cgroup_move_lists() is called from mem_cgroup_isolate_pages() and
mem_cgroup_move_lists(). In mem_cgroup_move_lists(), we have the page_cgroup
lock. I think the current code works on the assumption (although not documented
anywhere I've seen), that PAGE_CGROUP_FLAG_INACTIVE/ACTIVE/UNEVICTABLE bits are
protected by lru_lock. Please look at

__mem_cgroup_remove_list
__mem_cgroup_add_list
__mem_cgroup_move_lists
__mem_cgroup_charge_common (sets this flag, before the pc is associated with the
page).

Am I missing something (today is holiday here, so I am in a bit of a lazy/sleepy
mood :) )

-- 
	Balbir
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