Re: A unresponsive file system can hang all I/O in the system onlinux-2.6.23-rc6 (dirty_thresh problem?)

From: Andrew Morton
Date: Fri Sep 28 2007 - 16:12:05 EST

On Fri, 28 Sep 2007 15:52:28 -0400
Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote:

> 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@xxxxxxxxxx> 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.

hm, so ext3 got stuck in nfs via __alloc_pages direct reclaim?

We should be able to fix that by marking the backing device as
write-congested. That'll have small race windows, but it should be a 99.9%

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