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

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Message-ID: <1b4283da-44df-4a02-3167-e295243cef78@deltatee.com>
Date:   Wed, 5 Sep 2018 13:33:23 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>
Cc:     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 05/09/18 01:26 PM, Jens Axboe wrote:
> On 9/3/18 4:26 PM, Logan Gunthorpe wrote:
>> I personally agree with Christoph. But if there's consensus in the other
>> direction or this is a real blocker moving this forward, I can remove it
>> for the next version.
> 
> It's a simple branch because the check isn't exhaustive. It just checks
> the first page. At that point you may as well just require the caller to
> flag the bio/rq as being P2P, and then do a check for P2P compatibility
> with the queue.

Hmm, we had something like that in v4[1] but it just seemed redundant to
create a flag when the information was already in the bio and kind of
ugly for the caller to check for, then set, the flag. I'm not _that_
averse to going back to that though...

Logan

[1]
https://lore.kernel.org/lkml/20180423233046.21476-8-logang@deltatee.com/T/#u