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

[Andrew Morton]

On Thu, 23 Jan 2014 09:59:06 +0400 Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote:

> On Wed, Jan 22, 2014 at 02:45:53PM -0800, Andy Lutomirski wrote:
> > >     
> > >     Thus when user space application track memory changes now it can detect if
> > >     vma area is renewed.
> > 
> > Presumably some path is failing to set VM_SOFTDIRTY, thus preventing mms
> > from being merged.
> > 
> > That being said, this could cause vma blowups for programs that are
> > actually using this thing.
> 
> Hi Andy, indeed, this could happen. The easiest way is to ignore softdirty bit
> when we're trying to merge vmas and set it one new merged. I think this should
> be correct. Once I finish I'll send the patch.

Hang on.  We think the problem is that gimp is generating vmas which
*should* be merged, but for unknown reasons they differ in
VM_SOFTDIRTY, yes?

Shouldn't we work out where we're forgetting to set VM_SOFTDIRTY? 
Putting bandaids over this error when we come to trying to merge the
vmas sounds very wrong?
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