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

Peter Zijlstra
2009-12-17T08:46:21Z

On Thu, 2009-12-17 at 09:40 +0100, Andi Kleen wrote:
> On Wed, Dec 16, 2009 at 11:57:04PM +0100, Peter Zijlstra wrote:
> > On Wed, 2009-12-16 at 19:31 +0900, KAMEZAWA Hiroyuki wrote:
> >
> > > The problem of range locking is more than mmap_sem, anyway. I don't think
> > > it's possible easily.
> >
> > We already have a natural range lock in the form of the split pte lock.
> >
> > If we make the vma lookup speculative using RCU, we can use the pte lock
>
> One problem is here that mmap_sem currently contains sleeps
> and RCU doesn't work for blocking operations until a custom
> quiescent period is defined.

Right, so one thing we could do is always have preemptible rcu present
in another RCU flavour, like

rcu_read_lock_sleep()
rcu_read_unlock_sleep()
call_rcu_sleep()

or whatever name that would be, and have PREEMPT_RCU=y only flip the
regular rcu implementation between the sched/sleep one.