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SubjectRe: [PATCH 14/20] mm: Remove i_mmap_lock lockbreak
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On Tue, 2011-04-19 at 13:07 -0700, Andrew Morton wrote:
> On Fri, 01 Apr 2011 14:13:12 +0200
> Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
>
> > Hugh says:
> > "The only significant loser, I think, would be page reclaim (when
> > concurrent with truncation): could spin for a long time waiting for
> > the i_mmap_mutex it expects would soon be dropped? "
> >
> > Counter points:
> > - cpu contention makes the spin stop (need_resched())
> > - zap pages should be freeing pages at a higher rate than reclaim
> > ever can
> >
> > I think the simplification of the truncate code is definately worth it.
>
> Well, we don't need to guess. These things are testable!

I suppose you're right, but I'm having a bit of a hard time coming up
with a sensible (reproducible) test case for the page reclaim part of
this problem set.

I'll try running 3 cyclic file scanners sized such that 2 exceed the
memory footprint of the machine and truncate the 3rd's file after
warming up.

That is, unless someone has a saner idea..



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