linux-kernel - Re: [Bug 67651] Bisected: Lots of fragmented mmaps cause gimp to fail in 3.12 after exceeding vm_max_map

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Message-Id: <20140122220910.198121ee.akpm@linux-foundation.org>
Date:	Wed, 22 Jan 2014 22:09:10 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Mel Gorman <mgorman@...e.de>,
	Pavel Emelyanov <xemul@...allels.com>, gnome@...t.net,
	drawoc@...krefraction.com, alan@...rguk.ukuu.org.uk,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	bugzilla-daemon@...zilla.kernel.org
Subject: Re: [Bug 67651] Bisected: Lots of fragmented mmaps cause gimp to
 fail in 3.12 after exceeding vm_max_map_count

On Thu, 23 Jan 2014 09:59:06 +0400 Cyrill Gorcunov <gorcunov@...il.com> 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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