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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id r4sm69930362qta.93.2019.08.13.04.57.07 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 13 Aug 2019 04:57:07 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hxVQJ-0007sn-HH; Tue, 13 Aug 2019 08:57:07 -0300 Date: Tue, 13 Aug 2019 08:57:07 -0300 From: Jason Gunthorpe To: Jason Wang Cc: "Michael S. Tsirkin" , 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 Message-ID: <20190813115707.GC29508@ziepe.ca> References: <20190809054851.20118-1-jasowang@redhat.com> <20190810134948-mutt-send-email-mst@kernel.org> <360a3b91-1ac5-84c0-d34b-a4243fa748c4@redhat.com> <20190812054429-mutt-send-email-mst@kernel.org> <20190812130252.GE24457@ziepe.ca> <9a9641fe-b48f-f32a-eecc-af9c2f4fbe0e@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9a9641fe-b48f-f32a-eecc-af9c2f4fbe0e@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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