linux-kernel - Re: nfsd deadlock, 2.6.36-rc3

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Date:	Wed, 8 Sep 2010 13:50:32 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Tim Gardner <tim.gardner@...onical.com>
Cc:	Neil Brown <neilb@...e.de>, linux-nfs@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Trond.Myklebust@...app.com
Subject: Re: nfsd deadlock, 2.6.36-rc3

On Wed, Sep 08, 2010 at 10:52:51AM -0600, Tim Gardner wrote:
> The solution appears to be to twiddle with
> /proc/sys/vm/min_free_kbytes and /proc/sys/vm/drop_caches, though
> I'm not sure this addresses the root cause. Perhaps low memory
> really is the root cause.
> 
> At any rate, their solution was to set min_free_kbytes to 4GB, and
> to 'echo 1 > /proc/sys/vm/drop_caches' whenever free memory fell
> below 8GB. Not particularly elegant, but it appears to have stopped
> their server from wedging.

That does sound like a workaround rather than a fix.  Were there any
diagnostics left in the logs after the lockups?  Could you get sysrq-t
dumps and figure out what was waiting on what?  If the system was too
wedged for any of that to work, would any fo the watchdog deubgging
options help?

--b.
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