Re: [Bug 67651] Bisected: Lots of fragmented mmaps cause gimp tofail in 3.12 after exceeding vm_max_map_count

From: Mel Gorman
Date: Thu Jan 23 2014 - 05:30:53 EST

On Thu, Jan 23, 2014 at 02:33:25AM +0400, Cyrill Gorcunov wrote:
> On Wed, Jan 22, 2014 at 11:19:28PM +0400, Cyrill Gorcunov wrote:
> > > commit. Test case was simple -- try and open the large file described in
> > > the bug. I did not investigate the patch itself as I'm just reporting
> > > the results of the bisection. If I had to guess, I'd say that VMA
> > > merging has been affected.
> >
> > Thanks a lot for report, Mel! I'm investigating...
> Mel, here is a quick fix for bring merging back (just in case if you
> have a minute to test it and confirm the merging were affected). It
> seems I've lost setting up vma-softdirty bit somewhere and procedure
> which tests vma flags mathcing fails, will continue investigating/testing
> tomorrow.

The test case passes with this patch applied to 3.13 so that appears
to confirm that this is related to VM_SOFTDIRTY preventing merges.
Unfortunately I did not have slabinfo tracking enabled to double check
the number of vm_area_structs in teh system.

Mel Gorman
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