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SubjectRe: long sleep_on_page delays writing to slow storage
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



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