Messages in this thread | | | From | Jann Horn <> | Date | Thu, 27 Jul 2023 17:15:45 +0200 | Subject | Re: [PATCH 0/2] fix vma->anon_vma check for per-VMA locking; fix anon_vma memory ordering |
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On Thu, Jul 27, 2023 at 5:07 PM Matthew Wilcox <willy@infradead.org> wrote: > On Thu, Jul 27, 2023 at 04:39:34PM +0200, Jann Horn wrote: > > The other option is to replace the READ_ONCE() with a > > smp_load_acquire(), at which point it becomes a lot simpler to show > > that the code is correct. > > Aren't we straining at gnats here? The context of this is handling a > page fault, and we used to take an entire rwsem for read. I'm having > a hard time caring about "the extra expense" of an unnecessarily broad > barrier. > > Cost of an L3 cacheline miss is in the thousands of cycles. Cost of a > barrier is ... tens?
Yeah, fair point. If it's hard to show correctness with READ_ONCE() we can just use smp_load_acquire() and call it a day.
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