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Date: Thu, 30 Aug 2018 13:19:25 -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 1:17 PM, Logan Gunthorpe wrote: > > > On 30/08/18 01:11 PM, Jens Axboe wrote: >> 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. > > Well, the point was to prevent driver writers from doing the wrong > thing. The WARN_ON would be a bit pointless in the driver if we rely on > the driver to either do the right thing or add the WARN_ON themselves. > > If I'm going to change anything I'd drop the warning entirely and move > the NO_MERGE back into the caller... Of course, if you move it into the caller, the warning makes no sense. > Note: the check will be compiled out if the kernel does not support PCI P2P. Sure, but then distros tend to enable everything... -- Jens Axboe
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