Messages in this thread | | | Subject | Re: [RFC v1][PATCH]page_fault retry with NOPAGE_RETRY | From | Peter Zijlstra <> | Date | Thu, 27 Nov 2008 11:00:07 +0100 |
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On Thu, 2008-11-27 at 01:28 -0800, Mike Waychison wrote:
> Correct. I don't recall the numbers from the pathelogical cases we were > seeing, but iirc, it was on the order of 10s of seconds, likely > exascerbated by slower than usual disks. I've been digging through my > inbox to find numbers without much success -- we've been using a variant > of this patch since 2.6.11.
> We generally try to avoid such things, but sometimes it a) can't be > easily avoided (third party libraries for instance) and b) when it hits > us, it affects the overall health of the machine/cluster (the monitoring > daemons get blocked, which isn't very healthy).
If its only monitoring, there might be another solution. If you can keep the required data in a separate (approximate) copy so that you don't need mmap_sem at all to show them.
If your mmap_sem is so contended your latencies are unacceptable, adding more users to it - even statistics gathering, just isn't going to cure the situation.
Furthermore, /proc code usually isn't written with performance in mind, so its usually simple and robust code. Adding it to a 'hot'-path like you're doing doesn't seem advisable.
Also, releasing and re-acquiring mmap_sem can significantly add to the cacheline bouncing that thing already has.
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