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Subject: Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and
 check support for requests
To:     Christoph Hellwig <hch@lst.de>
Cc:     Logan Gunthorpe <logang@deltatee.com>,
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        Bjorn Helgaas <bhelgaas@google.com>,
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        Max Gurtovoy <maxg@mellanox.com>,
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        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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 <09258b9b-3aed-9890-b31a-bd70a133966c@kernel.dk>
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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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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