On Thu, Jan 31, 2008 at 06:39:19PM -0800, Christoph Lameter wrote:
> On Thu, 31 Jan 2008, Robin Holt wrote:
>
> > Jack has repeatedly pointed out needing an unregister outside the
> > mmap_sem. I still don't see the benefit to not having the lock in the mm.
>
> I never understood why this would be needed. ->release removes the
> mmu_notifier right now.
Christoph -
We discussed this earlier this week. Here is part of the mail:
------------
> > There currently is no __mmu_notifier_unregister(). Oversite???
>
> No need. mmu_notifier_release implies an unregister and I think that is
> the most favored way to release resources since it deals with the RCU
> quiescent period.
I currently unlink the mmu_notifier when the last GRU mapping is closed. For
example, if a user does a:
gru_create_context();
...
gru_destroy_context();
the mmu_notifier is unlinked and all task tables allocated
by the driver are freed. Are you suggesting that I leave tables
allocated until the task terminates??
Why is that better? What problem do I cause by trying
to free tables as soon as they are not needed?
-----------------------------------------------
> Christoph responded:
> > the mmu_notifier is unlinked and all task tables allocated
> > by the driver are freed. Are you suggesting that I leave tables
> > allocated until the task terminates??
>
> You need to leave the mmu_notifier structure allocated until the next
> quiescent rcu period unless you use the release notifier.
I assumed that I would need to use call_rcu() or synchronize_rcu()
before the table is actually freed. That's still on my TODO list.
--- jack
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