linux-kernel - Re: [PATCH 0/6] mempolicy memory corruption fixlet

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Message-ID: <20120530212235.GB20051@decadent.org.uk>
Date:	Wed, 30 May 2012 22:22:36 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Christoph Lameter <cl@...ux.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...gle.com>, Dave Jones <davej@...hat.com>,
	Mel Gorman <mgorman@...e.de>, stable@...r.kernel.org,
	hughd@...gle.com, sivanich@....com
Subject: Re: [PATCH 0/6] mempolicy memory corruption fixlet

On Wed, May 30, 2012 at 04:00:55PM -0400, KOSAKI Motohiro wrote:
> On Wed, May 30, 2012 at 3:52 PM, Andi Kleen <andi@...stfloor.org> wrote:
> > On Wed, May 30, 2012 at 02:42:42PM -0500, Christoph Lameter wrote:
> >> On Wed, 30 May 2012, Andi Kleen wrote:
> >>
> >> > On Wed, May 30, 2012 at 01:50:02PM -0500, Christoph Lameter wrote:
> >> > > On Wed, 30 May 2012, Andi Kleen wrote:
> >> > >
> >> > > > I always regretted that cpusets were no done with custom node lists.
> >> > > > That would have been much cleaner and also likely faster than what we have.
> >> > >
> >> > > Could shared memory policies ignore cpuset constraints?
> >> >
> >> > Only if noone uses cpusets as a "security" mechanism, just for a "soft policy"
> >> > Even with soft policy you could well break someone's setup.
> >>
> >> Well at least lets exempt shared memory from memory migration and memory
> >> policy updates. That seems to be causing many of these issues.
> >
> > Migration on the page level is needed for the memory error handling.
> >
> > Updates: you mean not allowing to set the policy when there are already
> > multiple mappers? I could see that causing some unexpected behaviour. Presumably
> > a standard database will only set it at the beginning, but I don't know
> > if that would work for all users.
> 
> We don't need to kill migration core. We only need to kill that mbind(2) updates
> vma->policy of shmem.
[...]

So should I (and Greg) drop 'mm: mempolicy: Let vma_merge and
vma_split handle vma->vm_policy linkages' from the pending stable
releases?  Or is that OK as an interim fix until these changes go
into mainline?
 
Ben.

-- 
Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
                                                              - Albert Camus
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