Messages in this thread | | | Subject | Re: [PATCH V5 0/9] Fixes for vhost metadata acceleration | From | Jason Wang <> | Date | Thu, 15 Aug 2019 11:26:46 +0800 |
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On 2019/8/13 下午7:57, Jason Gunthorpe wrote: > On Tue, Aug 13, 2019 at 04:31:07PM +0800, Jason Wang wrote: > >> What kind of issues do you see? Spinlock is to synchronize GUP with MMU >> notifier in this series. > A GUP that can't sleep can't pagefault which makes it a really weird > pattern
My understanding is __get_user_pages_fast() assumes caller can fail or have fallback. And we have graceful fallback to copy_{to|from}_user().
> >> Btw, back to the original question. May I know why synchronize_rcu() is not >> suitable? Consider: > We already went over this. You'd need to determine it doesn't somehow > deadlock the mm on reclaim paths. Maybe it is OK, the rcq_gq_wq is > marked WQ_MEM_RECLAIM at least..
Yes, will take a look at this.
> > I also think Michael was concerned about the latency spikes a long RCU > delay would cause.
I don't think it's a real problem consider MMU notifier could be preempted or blocked.
Thanks
> > Jason
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