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

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 28 Sep 2007 15:16:11 -0400 Trond Myklebust <trond.myklebust@fys.uio.no> wrote:

> On Fri, 2007-09-28 at 11:49 -0700, Andrew Morton wrote:
> > On Fri, 28 Sep 2007 13:00:53 -0400 Trond Myklebust <trond.myklebust@fys.uio.no> wrote:
> > > 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)
> 
> 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?

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.