Re: [PATCH] mmu notifiers #v6

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).

Thanks! Yes the seqlock you are using now ends up looking similar
to what I did and I couldn't find a hole in that either. So I
think this is going to work.

I do prefer some parts of my patch, however for everyone's sanity,
I think you should be the maintainer of the mmu notifiers, and I
will send you incremental changes that can be discussed more easily
that way (nothing major, mainly style and minor things).

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.

I agree: your coherent, non-sleeping mmu notifiers are pretty simple
and unintrusive. The sleeping version is fundamentally going to either
need to change VM locks, or be non-coherent, so I don't think there is
a question of making one solution fit everybody. So the sleeping /
xrmap patch should be kept either completely independent, or as an
add-on to this one.

I will post some suggestions to you when I get a chance.

 

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>