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Subject: Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and
 check support for requests
References: <20180830185352.3369-1-logang@deltatee.com>
 <20180830185352.3369-8-logang@deltatee.com>
 <b5ab8fa3-34ac-3117-fa0d-5206c3939435@kernel.dk>
 <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 <axboe@kernel.dk>
Message-ID: <bcc1b3cf-2fd9-fa61-9cfb-b0e4d84e5d94@kernel.dk>
Date: Wed, 5 Sep 2018 13:54:31 -0600
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To: Christoph Hellwig <hch@lst.de>
Cc: Alex Williamson <alex.williamson@redhat.com>, linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>, Jason Gunthorpe <jgg@mellanox.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Bjorn Helgaas <bhelgaas@google.com>, Max Gurtovoy <maxg@mellanox.com>, =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
List-ID: <linux-nvdimm@lists.01.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

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