Re: long sleep_on_page delays writing to slow storage

[Dave Jones <davej@redhat.com>]

On Thu, Nov 10, 2011 at 10:34:42AM +0100, Johannes Weiner wrote:
 
 > > I wonder if a change like this would be enough?
 > > 
 > >        sync_migration = !(gfp_mask & __GFP_NO_KSWAPD);
 > > 
 > > But even if hidden in a new function, the main downside overall is the
 > > fact we'll pass one more var through the stack of fast paths.
 > > 
 > > Johannes I recall you reported this too and Mel suggested the above
 > > change, did it help in the end?
 > 
 > Yes, it completely fixed the latency problem.
 > 
 > That said, I haven't looked at the impact on the THP success rate, but
 > a regression there is probably less severe than half-minute-stalls in
 > interactive applications.

FWIW, we've had a few reports from Fedora users since we moved to 3.x kernels
about similar problems, so whatever the fix is for this should probably
go to stable too.

I could push an update for Fedora users to test the change above if
that would be helpful ?

	Dave