linux-kernel - Re: [patch] rt: res

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Message-Id: <20090213085640.704caf34.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 13 Feb 2009 08:56:40 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...x.de>,
	LKML <linux-kernel@...r.kernel.org>,
	rt-users <linux-rt-users@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Carsten Emde <ce@...g.ch>, Clark Williams <williams@...hat.com>
Subject: Re: [patch] rt: res_counter fix, v2

On Thu, 12 Feb 2009 22:28:33 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> * Ingo Molnar <mingo@...e.hu> [2009-02-12 12:28:54]:
> 
> > 
> > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > 
> > > On Thu, 12 Feb 2009 11:21:13 +0100
> > > Ingo Molnar <mingo@...e.hu> wrote:
> > The question is, are these local IRQ flags manipulations really needed
> > in this code, and if yes, why?
> 
> We needed the local IRQ flags, since these counters are updated from
> page fault context and from reclaim context with lru_lock held with
> IRQ's disabled. I've been thinking about replacing the spin lock with
> seq lock, but have not gotten to it yet.
> 
Hmm ?  I can't understand. Why we have to disable IRQ here again ?
And,
  - try_to_unmap() is called in shrink_page_list(),  there, no zone->lru_lock.
  - page fault path doesn't hold zone->lru_lock.

My concern is only shmem. But I think it doesn't call charge() within lock, actually.

Thanks,
-Kame

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