From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E8F1AC43334 for ; Wed, 5 Sep 2018 20:10:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9EB2F2073D for ; Wed, 5 Sep 2018 20:10:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9EB2F2073D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=deltatee.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727980AbeIFAmK (ORCPT ); Wed, 5 Sep 2018 20:42:10 -0400 Received: from ale.deltatee.com ([207.54.116.67]:53816 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727688AbeIFAmJ (ORCPT ); Wed, 5 Sep 2018 20:42:09 -0400 Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtp (Exim 4.89) (envelope-from ) id 1fxe7h-0005Wq-UG; Wed, 05 Sep 2018 14:09:58 -0600 To: Christoph Hellwig , Jens Axboe Cc: 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> <20180905201152.GA1893@lst.de> From: Logan Gunthorpe Message-ID: Date: Wed, 5 Sep 2018 14:09:55 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180905201152.GA1893@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: christian.koenig@amd.com, alex.williamson@redhat.com, benh@kernel.crashing.org, jglisse@redhat.com, dan.j.williams@intel.com, maxg@mellanox.com, jgg@mellanox.com, bhelgaas@google.com, sagi@grimberg.me, keith.busch@intel.com, sbates@raithlin.com, linux-block@vger.kernel.org, linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, axboe@kernel.dk, hch@lst.de X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and check support for requests X-SA-Exim-Version: 4.2.1 (built Tue, 02 Aug 2016 21:08:31 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/09/18 02:11 PM, Christoph Hellwig wrote: > On Wed, Sep 05, 2018 at 01:54:31PM -0600, Jens Axboe wrote: >> 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? > > Just an additional little safe guard. If you think it isn't worth > it I guess we can just drop it for now. Yes, the point is to prevent driver writers from doing the wrong thing by not doing the necessary checks before submitting to the queue. Logan