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 - 14:50:20 EST
On Fri, 28 Sep 2007 13:00:53 -0400 Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote:
> On Thu, 2007-09-27 at 23:50 -0700, Andrew Morton wrote:
> > Actually we perhaps could address this at the VFS level in another way.
> > Processes which are writing to the dead NFS server will eventually block in
> > balance_dirty_pages() once they've exceeded the memory limits and will
> > remain blocked until the server wakes up - that's the behaviour we want.
> > What we _don't_ want to happen is for other processes which are writing to
> > other, non-dead devices to get collaterally blocked. We have patches which
> > might fix that queued for 2.6.24. Peter?
> Do these patches also cause the memory reclaimers to steer clear of
> devices that are congested (and stop waiting on a congested device if
> they see that it remains congested for a long period of time)? Most of
> the collateral blocking I see tends to happen in memory allocation...
No, they don't attempt to do that, but I suspect they put in place
infrastructure which could be used to improve direct-reclaimer latency. In
the throttle_vm_writeout() path, at least.
Do you know where the stalls are occurring? throttle_vm_writeout(), or via
direct calls to congestion_wait() from page_alloc.c and vmscan.c? (running
sysrq-w five or ten times will probably be enough to determine this)
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