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Wed, 05 Sep 2018 12:54:33 -0700 (PDT) Subject: Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and check support for requests To: Christoph Hellwig Cc: Logan Gunthorpe , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, Stephen Bates , Keith Busch , Sagi Grimberg , Bjorn Helgaas , Jason Gunthorpe , Max Gurtovoy , Dan Williams , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Benjamin Herrenschmidt , Alex Williamson , =?UTF-8?Q?Christian_K=c3=b6nig?= References: <20180830185352.3369-1-logang@deltatee.com> <20180830185352.3369-8-logang@deltatee.com> <20180901082812.GB670@lst.de> <5f79c012-c6e1-56bb-62fd-0689181fb2c9@deltatee.com> <59b28977-8f2a-6228-2050-03fae6bdbedd@kernel.dk> <1b4283da-44df-4a02-3167-e295243cef78@deltatee.com> <09258b9b-3aed-9890-b31a-bd70a133966c@kernel.dk> <20180905195647.GA1626@lst.de> From: Jens Axboe Message-ID: Date: Wed, 5 Sep 2018 13:54:31 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <20180905195647.GA1626@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/5/18 1:56 PM, Christoph Hellwig wrote: > On Wed, Sep 05, 2018 at 01:45:04PM -0600, Jens Axboe wrote: >> The point is that the caller doesn't necessarily know where the bio >> will end up, hence the caller can't fully check if the whole stack >> supports P2P. > > The caller must necessarily know where the bio will end up, as for P2P > support we need to query if the bio target is P2P capable vs the > source of the P2P memory. Then what's the point of having the check at all? -- Jens Axboe