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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Date:	Fri, 28 Sep 2007 15:52:28 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Chakri n <chakriin5@...il.com>,
	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>
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, 2007-09-28 at 12:26 -0700, Andrew Morton wrote:
> On Fri, 28 Sep 2007 15:16:11 -0400 Trond Myklebust <trond.myklebust@....uio.no> wrote:
> > Looking back, they were getting caught up in
> > balance_dirty_pages_ratelimited() and friends. See the attached
> > example...
> 
> that one is nfs-on-loopback, which is a special case, isn't it?

I'm not sure that the hang that is illustrated here is so special. It is
an example of a bog-standard ext3 write, that ends up calling the NFS
client, which is hanging. The fact that it happens to be hanging on the
nfsd process is more or less irrelevant here: the same thing could
happen to any other process in the case where we have an NFS server that
is down.

> NFS on loopback used to hang, but then we fixed it.  It looks like we
> broke it again sometime in the intervening four years or so.

It has been quirky all through the 2.6.x series because of this issue.

Cheers
  Trond

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