linux-kernel - Re: Processes spinning forever, apparently in lock_timer

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Date:	Fri, 21 Sep 2007 12:16:34 -0400
From:	Chuck Ebbert <cebbert@...hat.com>
To:	Hugh Dickins <hugh@...itas.com>
CC:	Andy Whitcroft <apw@...dowen.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthias Hensler <matthias@...se.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	richard kennedy <richard@....demon.co.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Processes spinning forever, apparently in lock_timer_base()?

On 09/21/2007 11:58 AM, Hugh Dickins wrote:
> Looking at the 2.6.18-2.6.23 code, I'm uncertain what to try instead.
> There is a refresh_vm_stats function which we could call (then retest
> the break condition) just before resorting to congestion_wait.  But
> the big NUMA people might get very upset with me calling that too
> often: causing a thundering herd of bouncing cachelines which that
> was all designed to avoid.  And it's not obvious to me what condition
> to test for dirty_thresh "too low".
> 
> I believe Peter gave all this quite a lot of thought when he was
> making the rc6-mm1 changes, and I'd rather defer to him for a
> suggestion of what best to do in earlier releases.  Or maybe he'll
> just point out how this couldn't have been a problem before.
> 
> Or there is is Richard's patch, which I haven't considered, but
> Andrew was not quite satisfied with it - partly because he'd like
> to understand how the situation could come about first, perhaps
> we have now got an explanation.
> 

My patch is just Richard's with the added requirement that we loop
some minimum number of times before exiting balance_dirty_pages()
with unfinished work.

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