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
