Re: [PATCH V5 0/9] Fixes for vhost metadata acceleration

Jason Gunthorpe
2019-08-13T11:57:14Z

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

> 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..

I also think Michael was concerned about the latency spikes a long RCU
delay would cause.

Jason