linux-kernel - Re: [mm][RFC][PATCH 0/11] mm accessor updates.

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Date:	Thu, 17 Dec 2009 09:41:39 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...e.hu" <mingo@...e.hu>, minchan.kim@...il.com
Subject: Re: [mm][RFC][PATCH 0/11] mm accessor updates.

On Thu, Dec 17, 2009 at 12:01:55AM +0100, Peter Zijlstra wrote:
> On Wed, 2009-12-16 at 10:27 -0600, Christoph Lameter wrote:
> > On Wed, 16 Dec 2009, Andi Kleen wrote:
> > 
> > > > Do you have alternative recommendation rather than wrapping all accesses by
> > > > special functions ?
> > >
> > > Work out what changes need to be done for ranged mmap locks and do them all
> > > in one pass.
> > 
> > Locking ranges is already possible through the split ptlock and
> > could be enhanced through placing locks in the vma structures.
> > 
> > That does nothing solve the basic locking issues of mmap_sem. We need
> > Kame-sans abstraction layer. A vma based lock or a ptlock still needs to
> > ensure that the mm struct does not vanish while the lock is held.
> 
> It should, you shouldn't be able to remove a mm while there's still
> vma's around, and you shouldn't be able to remove a vma when there's
> still pagetables around. And if you rcu-free all of them you're stable
> enough for lots of speculative behaviour.

Yes, the existing reference counts are probably sufficient for all that.

Still need list stability.

> As for per-vma locks, those are pretty much useless too, there's plenty
> applications doing lots of work on a few very large vmas.

True.
-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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