linux-kernel - Re: [RFC PATCH -v3] take all anon_vma locks in anon_vma

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Date:	Thu, 29 Apr 2010 08:37:26 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH -v3] take all anon_vma locks in anon_vma_lock

On Thu, Apr 29, 2010 at 09:28:25AM +0900, Minchan Kim wrote:
> On Thu, Apr 29, 2010 at 5:57 AM, Rik van Riel <riel@...hat.com> wrote:
> > Take all the locks for all the anon_vmas in anon_vma_lock, this properly
> > excludes migration and the transparent hugepage code from VMA changes done
> > by mmap/munmap/mprotect/expand_stack/etc...
> >
> > Unfortunately, this requires adding a new lock (mm->anon_vma_chain_lock),
> > otherwise we have an unavoidable lock ordering conflict.  This changes the
> > locking rules for the "same_vma" list to be either mm->mmap_sem for write,
> > or mm->mmap_sem for read plus the new mm->anon_vma_chain lock.  This limits
> > the place where the new lock is taken to 2 locations - anon_vma_prepare and
> > expand_downwards.
> >
> > Document the locking rules for the same_vma list in the anon_vma_chain and
> > remove the anon_vma_lock call from expand_upwards, which does not need it.
> >
> > Signed-off-by: Rik van Riel <riel@...hat.com>
> 
> This patch makes things simple. So I like this.

Agreed.

> Actually, I wanted this all-at-once locks approach.
> But I was worried about that how the patch affects AIM 7 workload
> which is cause of anon_vma_chain about scalability by Rik.

I had similar concerns. I'm surprised how it worked out.

> But now Rik himself is sending the patch. So I assume the patch
> couldn't decrease scalability of the workload heavily.
> 
> Let's wait result of test if Rik doesn't have a problem of AIM7.
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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