linux-kernel - Re: [PATCH] memcg: update documentation v5

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Date:	Tue, 13 Apr 2010 11:16:45 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memcg: update documentation v5

On Tue, Apr 13, 2010 at 08:38:43PM +0530, Balbir Singh wrote:
> * Vivek Goyal <vgoyal@...hat.com> [2010-04-13 10:03:02]:
> 
> > On Tue, Apr 13, 2010 at 09:57:18AM -0400, Vivek Goyal wrote:
> > > On Tue, Apr 13, 2010 at 01:45:53PM +0900, KAMEZAWA Hiroyuki wrote:
> > > 
> > 
> > Typed wrong email id last time and mail bounced. So here is another
> > attempt.
> > 
> > > [..]
> > > > -2. Locking
> > > > +2.6 Locking
> > > >  
> > > > -The memory controller uses the following hierarchy
> > > > +   lock_page_cgroup()/unlock_page_cgroup() should not be called under
> > > > +   mapping->tree_lock.
> > > >  
> > > 
> > > Because I never understood very well, I will ask. Why lock_page_cgroup()
> > > should not be called under mapping->tree_lock?
> > > 
> 
> The closest reference I can find to a conversation regarding this is
> 
> http://linux.derkeiler.com/Mailing-Lists/Kernel/2009-05/msg05158.html
> 

Thanks Balbir. So basically idea is that page_cgroup_lock() does not
disable interrupts hence can be interrupted. So don't do
lock_page_cgroup() in interrupt context at all otherwise it can lead to
various kind of deadlock scenarios.

One of those scenarios is lock_page_cgroup() under mapping->tree_lock.

That helps. Thanks

Vivek

> -- 
> 	Three Cheers,
> 	Balbir
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