Re: [PATCH 14/20] mm: Remove i_mmap_lock lockbreak

[Peter Zijlstra]

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@xxxxxxxxx> 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..

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/