On 7/16/07, Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:
- if (notify_on_release(cont)) {
+ if (atomic_dec_and_test(&css->refcnt) && notify_on_release(cont)) {
This seems like a good idea, as long as atomic_dec_and_test() isn't
noticeably more expensive than atomic_dec(). I assume it shouldn't
need to be, since the bus locking operations are presumably the same
in each case.
mutex_lock(&container_mutex);
set_bit(CONT_RELEASABLE, &cont->flags);
- if (atomic_dec_and_test(&css->refcnt)) {
- check_for_release(cont);
- }
+ check_for_release(cont);
mutex_unlock(&container_mutex);
That way we set the CONT_RELEASABLE bit only when the ref count drops
to zero.
That's probably a good idea, in conjunction with another part of my
patch for this that frees container objects under RCU - as soon as you
do the atomic_dec_and_test(), then in theory some other thread could
delete the container (since we're no longer going to be taking
container_mutex in this function). But as long as the container object
remains valid until synchronize_rcu() completes, then we can safely
set the CONT_RELEASABLE bit on it.
Yes, that is correct, the advantage is that with can_destroy() we
don't need to go through release synchronization each time we do
a css_put().
I think the amount of release synchronization *needed* is going to be
the same whether you have the refcounting done in the subsystem or in
the framework. But I agree that right now we're doing one more atomic
op than we strictly need to, and can remove it.
Paul
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