On Fri, 2007-09-28 at 11:49 -0700, Andrew Morton wrote:
quoted text
> 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...

Cheers
  Trond