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

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Message-ID: <20100319024039.GH18054@balbir.in.ibm.com>
Date:	Fri, 19 Mar 2010 08:10:39 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrea Righi <arighi@...eler.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

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-03-19 10:23:32]:

> On Thu, 18 Mar 2010 21:58:55 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
> > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-03-18 13:35:27]:
> 
> > > Then, no probelm. It's ok to add mem_cgroup_udpate_stat() indpendent from
> > > mem_cgroup_update_file_mapped(). The look may be messy but it's not your
> > > fault. But please write "why add new function" to patch description.
> > > 
> > > I'm sorry for wasting your time.
> > 
> > Do we need to go down this route? We could check the stat and do the
> > correct thing. In case of FILE_MAPPED, always grab page_cgroup_lock
> > and for others potentially look at trylock. It is OK for different
> > stats to be protected via different locks.
> > 
> 
> I _don't_ want to see a mixture of spinlock and trylock in a function.
>

A well documented well written function can help. The other thing is to
of-course solve this correctly by introducing different locking around
the statistics. Are you suggesting the later?

-- 
	Three Cheers,
	Balbir
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