linux-kernel - Re: [PATCH -mmotm 1/5] memcg: disable irq at page cgroup lock

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Date:	Wed, 17 Mar 2010 17:28:55 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Andrea Righi <arighi@...eler.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Vivek Goyal <vgoyal@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andrew Morton <akpm@...ux-foundation.org>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -mmotm 1/5] memcg: disable irq at page cgroup lock

* Andrea Righi <arighi@...eler.com> [2010-03-15 00:26:38]:

> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> Now, file-mapped is maintaiend. But more generic update function
> will be needed for dirty page accounting.
> 
> For accountig page status, we have to guarantee lock_page_cgroup()
> will be never called under tree_lock held.
> To guarantee that, we use trylock at updating status.
> By this, we do fuzzy accounting, but in almost all case, it's correct.
>

I don't like this at all, but in almost all cases is not acceptable
for statistics, since decisions will be made on them and having them
incorrect is really bad. Could we do a form of deferred statistics and
fix this.

 
-- 
	Three Cheers,
	Balbir
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