Re: [PATCH] mmu notifiers #v6

[Robin Holt <holt@sgi.com>]

On Wed, Feb 20, 2008 at 11:39:42AM +0100, Andrea Arcangeli wrote:
> Given Nick's comments I ported my version of the mmu notifiers to
> latest mainline. There are no known bugs AFIK and it's obviously safe
> (nothing is allowed to schedule inside rcu_read_lock taken by
> mmu_notifier() with my patch).
> 
> XPMEM simply can't use RCU for the registration locking if it wants to
> schedule inside the mmu notifier calls. So I guess it's better to add
> the XPMEM invalidate_range_end/begin/external-rmap as a whole
> different subsystem that will have to use a mutex (not RCU) to
> serialize, and at the same time that CONFIG_XPMEM will also have to
> switch the i_mmap_lock to a mutex. I doubt xpmem fits inside a
> CONFIG_MMU_NOTIFIER anymore, or we'll all run a bit slower because of
> it. It's really a call of how much we want to optimize the MMU
> notifier, by keeping things like RCU for the registration.

But won't that other "subsystem" cause us to have two seperate callouts
that do equivalent things and therefore force a removal of this and go
back to what Christoph has currently proposed?

Robin