linux-kernel - Re: [PATCH 04/10] memcg: disable local interrupts in lock_page

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Date:	Thu, 7 Oct 2010 09:35:45 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Greg Thelen <gthelen@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	containers@...ts.osdl.org, Andrea Righi <arighi@...eler.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH 04/10] memcg: disable local interrupts in
 lock_page_cgroup()

On Wed, 6 Oct 2010 09:15:34 +0900
Minchan Kim <minchan.kim@...il.com> wrote:

> First of all, we could add your patch as it is and I don't expect any
> regression report about interrupt latency.
> That's because many embedded guys doesn't use mmotm and have a
> tendency to not report regression of VM.
> Even they don't use memcg. Hmm...
> 
> I pass the decision to MAINTAINER Kame and Balbir.
> Thanks for the detail explanation.
> 

Hmm. IRQ delay is a concern. So, my option is this. How do you think ?

1. remove local_irq_save()/restore() in lock/unlock_page_cgroup().
   yes, I don't like it.

2. At moving charge, do this:
	a) lock_page()/ or trylock_page()
	b) wait_on_page_writeback()
	c) do move_account under lock_page_cgroup().
	c) unlock_page()


Then, Writeback updates will never come from IRQ context while
lock/unlock_page_cgroup() is held by move_account(). There will be no race.

Do I miss something ?

Thanks,
-Kame

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