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

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...

Note: the check will be compiled out if the kernel does not support PCI P2P.