Re: [PATCH] anobjrmap 9 priority mjb tree

[Andrea Arcangeli <andrea@suse.de>]

On Thu, Apr 15, 2004 at 08:40:50AM -0700, Martin J. Bligh wrote:
> >> FYI, even without prio-tree, I get a 12% boost from converting i_shared_sem
> >> into a spinlock. I'll try doing the same on top of prio-tree next.
> > 
> > Good news, though not a surprise.
> > 
> > Any ideas how we might handle latency from vmtruncate (and
> > try_to_unmap) if using prio_tree with i_shared_lock spinlock?
> 
> I've been thinking about that. My rough plan is to go wild, naked and lockless.
> If we arrange things in the correct order, new entries onto the list would
> pick up the truncated image of the file (so they'd be OK). Entries removed
> from the list don't matter anyway. We just need to make sure that everything
> that was on the list when we start does get truncated.

entries removed must be freed with RCU, and that means vmas freed with
rcu that means mm and pgd freed with rcu and the whole vm will collapse
on you when you attempt that. I mean it's going all the way up to the
whole MM, not just the shared list of vmas.