linux-kernel - Re: [PATCH 18/19] x86, mpx: do not count MPX VMAs as neighbors when unmapping

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Message-ID: <alpine.DEB.2.11.1505182354010.4225@nanos>
Date:	Mon, 18 May 2015 23:54:15 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Hansen <dave@...1.net>
cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	dave.hansen@...ux.intel.com
Subject: Re: [PATCH 18/19] x86, mpx: do not count MPX VMAs as neighbors when
 unmapping

On Fri, 8 May 2015, Dave Hansen wrote:
> The comment pretty much says it all.
> 
> I wrote a test program that does lots of random allocations
> and forces bounds tables to be created.  It came up with a
> layout like this:
> 
>   ....   | BOUNDS DIRECTORY ENTRY COVERS |  ....
>          |    BOUNDS TABLE COVERS        |
> |  BOUNDS TABLE |  REAL ALLOC | BOUNDS TABLE |
> 
> Unmapping "REAL ALLOC" should have been able to free the
> bounds table "covering" the "REAL ALLOC" because it was the
> last real user.  But, the neighboring VMA bounds tables were
> found, considered as real neighbors, and we declined to free
> the bounds table covering the area.
> 
> Doing this over and over left a small but significant number
> of these orphans.  Handling them is fairly straighforward.
> All we have to do is walk the VMAs and skip all of the MPX
> ones when looking for neighbors.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
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