Messages in this thread | | | Date | Thu, 22 May 2014 17:04:51 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] mm: filemap: Avoid unnecessary barriers and waitqueue lookups in unlock_page fastpath v7 |
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On Thu, May 22, 2014 at 03:40:45PM +0100, Mel Gorman wrote:
> > +static bool __wake_up_common(wait_queue_head_t *q, unsigned int mode, > > int nr_exclusive, int wake_flags, void *key) > > { > > wait_queue_t *curr, *next; > > + bool woke = false; > > > > list_for_each_entry_safe(curr, next, &q->task_list, task_list) { > > unsigned flags = curr->flags; > > > > + if (curr->func(curr, mode, wake_flags, key)) { > > + woke = true; > > + if ((flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive) > > + break; > > + } > > } > > + > > + return woke; > > Ok, thinking about this more I'm less sure. > > There are cases where the curr->func returns false even though there is a > task that needs to run -- task was already running or preparing to run. We > potentially end up clearing PG_waiters while there are still tasks on the > waitqueue. As __finish_wait checks if the waitqueue is empty and the last > waiter clears the bit I think there is nothing to gain by trying to do the > same job in __wake_up_page_bit.
Hmm, I think you're right, we need the test result from wake_bit_function(), unpolluted by the ttwu return value. [unhandled content-type:application/pgp-signature] | |