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

Andi Kleen
2009-12-17T08:41:43Z

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@linux.intel.com -- Speaking for myself only.