Messages in this thread | | | Subject | Re: [PATCH] mm: thp: use down_read_trylock in khugepaged to avoid long block | From | "Yang Shi" <> | Date | Wed, 20 Dec 2017 09:35:39 +0800 |
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On 12/18/17 12:41 AM, Michal Hocko wrote: > On Sat 16-12-17 23:09:25, Kirill A. Shutemov wrote: >> On Sat, Dec 16, 2017 at 12:45:25PM +0100, Michal Hocko wrote: >>> On Sat 16-12-17 04:04:10, Yang Shi wrote: > [...] >>>> Shall we add "cond_resched()" in unmap_vmas(), i.e for every 100 vmas? It >>>> may improve the responsiveness a little bit for non-preempt kernel, although >>>> it still can't release the semaphore. >>> >>> We already do, once per pmd (see zap_pmd_range). >> >> It doesn't help. We would need to find a way to drop mmap_sem, if we're >> holding it way too long. And doing it on per-vma count basis is not right >> call. It won't address issue with single huge vma. > > Absolutely agreed. I just wanted to point out that a new cond_resched is > not really needed. One way to reduce the lock starvation is to use range > locking.
It looks the range locking development is stalled?
Yang
> >> Do we have any instrumentation that would help detect starvation on a >> rw_semaphore? > > I am afraid we don't. >
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