linux-kernel - Re: A unresponsive file system can hang all I/O in the system on linux-2.6.23-rc6 (dirty

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Message-Id: <20070928110445.69e687c0.akpm@linux-foundation.org>
Date:	Fri, 28 Sep 2007 11:04:45 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	corbet@....net (Jonathan Corbet)
Cc:	linux-pm <linux-pm@...ts.linux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>, nfs@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Chakri n" <chakriin5@...il.com>
Subject: Re: A unresponsive file system can hang all I/O in the system on
 linux-2.6.23-rc6 (dirty_thresh problem?)

On Fri, 28 Sep 2007 07:28:52 -0600 corbet@....net (Jonathan Corbet) wrote:

> Andrew wrote:
> > It's unrelated to the actual value of dirty_thresh: if the machine fills up
> > with dirty (or unstable) NFS pages then eventually new writers will block
> > until that condition clears.
> > 
> > 2.4 doesn't have this problem at low levels of dirty data because 2.4
> > VFS/MM doesn't account for NFS pages at all.
> 
> Is it really NFS-related?  I was trying to back up my 2.6.23-rc8 system
> to an external USB drive the other day when something flaked and the
> drive fell off the bus.  That, too, was sufficient to wedge the entire
> system, even though the only thing which needed the dead drive was one
> rsync process.  It's kind of a bummer to have to hit the reset button
> after the failure of (what should be) a non-critical piece of hardware.
> 
> Not that I have a fix to propose...:)
> 

That's a USB bug, surely.  What should happen is that the kernel attempts
writeback, gets an IO error and then your data gets lost.

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