Messages in this thread | | | Date | Sat, 1 Dec 2012 19:41:35 +0100 | From | Ingo Molnar <> | Subject | Re: [RFC PATCH] mm/migration: Remove anon vma locking from try_to_unmap() use |
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Sat, Dec 1, 2012 at 4:26 AM, Ingo Molnar <mingo@kernel.org> wrote: > > > > > > So as a quick concept hack I wrote the patch attached below. > > (It's not signed off, see the patch description text for the > > reason.) > > Well, it confirms that anon_vma locking is a big problem, but > as outlined in my other email it's completely incorrect from > an actual behavior standpoint.
Yeah.
> Btw, I think the anon_vma lock could be made a spinlock > instead of a mutex or rwsem, but that would probably take more > work. We *shouldn't* be doing anything that needs IO inside > the anon_vma lock, though, so it *should* be doable. But there > are probably quite a bit of allocations inside the lock, and I > know it covers huge areas, so a spinlock might not only be > hard to convert to, it quite likely has latency issues too.
I'll try the rwsem and see how it goes?
> Oh, btw, MUTEX_SPIN_ON_OWNER may well improve performance too, > but it gets disabled by DEBUG_MUTEXES. So some of the > performance impact of the vma locking may be *very* > kernel-config dependent.
Hm, indeed. For performance runs I typically disable lock debugging - which might have made me not directly notice some of the performance problems.
Thanks,
Ingo
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