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:   Thu, 30 Aug 2018 13:11:18 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Logan Gunthorpe <logang@...tatee.com>,
        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
Cc:     Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        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 8/30/18 12:53 PM, Logan Gunthorpe wrote:
> QUEUE_FLAG_PCI_P2P is introduced meaning a driver's request queue
> supports targeting P2P memory.
> 
> When a request is submitted we check if PCI P2PDMA memory is assigned
> to the first page in the bio. If it is, we ensure the queue it's
> submitted to supports it, and enforce REQ_NOMERGE.

I think this belongs in the caller - both the validity check, and
passing in NOMERGE for this type of request. I don't want to impose
this overhead on everything, for a pretty niche case.

-- 
Jens Axboe