Messages in this thread | | | Date | Sun, 15 Oct 2006 16:19:53 +0200 | From | Nick Piggin <> | Subject | Re: SPAM: Re: [patch 6/6] mm: fix pagecache write deadlocks |
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On Sun, Oct 15, 2006 at 03:51:09PM +0200, Peter Zijlstra wrote: > > > > > > > Why use raw {inc,dec}_preempt_count() and not > > > preempt_{disable,enable}()? Is the compiler barrier not needed here? And > > > do we really want to avoid the preempt_check_resched()? > > > > Counter to intuition, we actually don't mind being preempted here, > > but we do mind entering the (core) pagefault handler. Incrementing > > the preempt count causes the arch specific handler to bail out early > > before it takes any locks. > > > > Clear as mud? Wrapping it in a better name might be an improvement? > > Or wrapping it into the copy*user_atomic functions themselves (which > > is AFAIK the only place we use it). > > Right, but since you do inc the preempt_count you do disable preemption, > might as well check TIF_NEED_RESCHED when enabling preemption again.
Yeah, you are right about that. Unfortunately there isn't a good way to do this at the moment... well we could disable preempt around the section, but that would be silly for a PREEMPT kernel.
And we should really decouple it from preempt entirely, in case we ever want to check for it some other way in the pagefault handler.
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