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From: Jason Wang <jasowang@redhat.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH V5 0/9] Fixes for vhost metadata acceleration
Date: Thu, 15 Aug 2019 11:26:46 +0800	[thread overview]
Message-ID: <74838e61-3a5e-0f51-2092-f4a16d144b45@redhat.com> (raw)
In-Reply-To: <20190813115707.GC29508@ziepe.ca>


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


  parent reply	other threads:[~2019-08-15  3:26 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-09  5:48 [PATCH V5 0/9] Fixes for vhost metadata acceleration Jason Wang
2019-08-09  5:48 ` [PATCH V5 1/9] vhost: don't set uaddr for invalid address Jason Wang
2019-08-09  5:48 ` [PATCH V5 2/9] vhost: validate MMU notifier registration Jason Wang
2019-08-09  5:48 ` [PATCH V5 3/9] vhost: fix vhost map leak Jason Wang
2019-08-09  5:48 ` [PATCH V5 4/9] vhost: reset invalidate_count in vhost_set_vring_num_addr() Jason Wang
2019-08-09  5:48 ` [PATCH V5 5/9] vhost: mark dirty pages during map uninit Jason Wang
2019-08-09  5:48 ` [PATCH V5 6/9] vhost: don't do synchronize_rcu() in vhost_uninit_vq_maps() Jason Wang
2019-08-09  5:48 ` [PATCH V5 7/9] vhost: do not use RCU to synchronize MMU notifier with worker Jason Wang
2019-08-09  5:48 ` [PATCH V5 8/9] vhost: correctly set dirty pages in MMU notifiers callback Jason Wang
2019-08-09  5:48 ` [PATCH V5 9/9] vhost: do not return -EAGAIN for non blocking invalidation too early Jason Wang
2019-08-10 17:52 ` [PATCH V5 0/9] Fixes for vhost metadata acceleration Michael S. Tsirkin
2019-08-12  2:44   ` Jason Wang
2019-08-12  4:13     ` David Miller
2019-08-12  9:49     ` Michael S. Tsirkin
2019-08-12 13:02       ` Jason Gunthorpe
2019-08-13  8:31         ` Jason Wang
2019-08-13 11:57           ` Jason Gunthorpe
2019-08-13 16:41             ` Christoph Hellwig
2019-08-15  3:28               ` Jason Wang
2019-08-15  3:26             ` Jason Wang [this message]
2019-08-15 19:33               ` Jason Gunthorpe
2019-08-13  8:12       ` Jason Wang
2019-08-19 21:08         ` Michael S. Tsirkin
2019-08-20  2:29           ` Jason Wang
2019-09-01 18:02             ` Michael S. Tsirkin
  -- strict thread matches above, loose matches on Subject: below --
2019-08-07  7:06 [PATCH V4 0/9] Fixes for metadata accelreation Jason Wang
2019-08-07  7:06 ` [PATCH V4 7/9] vhost: do not use RCU to synchronize MMU notifier with worker Jason Wang
2019-08-07 12:07   ` Jason Gunthorpe
2019-08-07 14:02     ` Jason Wang
2019-08-08 12:54       ` Jason Wang
2019-08-10 19:12         ` [PATCH V5 0/9] Fixes for vhost metadata acceleration Michael S. Tsirkin

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