linux-kernel - Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and check support for requests

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Date:   Wed, 5 Sep 2018 21:56:47 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-rdma@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-block@...r.kernel.org, Stephen Bates <sbates@...thlin.com>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and
 check support for requests

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.