On Fri, Sep 21, 2018 at 08:15:50AM -0500, Bjorn Helgaas wrote: > On Wed, Sep 12, 2018 at 06:11:46PM -0600, Logan Gunthorpe wrote: > > The DMA address used when mapping PCI P2P memory must be the PCI bus > > address. Thus, introduce pci_p2pmem_map_sg() to map the correct > > addresses when using P2P memory. Memory mapped in this way does not > > need to be unmapped. > > I think the use of "map" in this context is slightly confusing because the > general expectation is that map/unmap must be balanced. > > I assume it's because the "mapping" consumes no resources, e.g., requires > no page table entries. Possibly there's a better verb than "map", e.g., > "convert", "convert_to_p2pdma", etc? > > If you keep "map", maybe add a sentence or two about why there's no > corresponding unmap? Another wrinkle is that "map" usually takes an A and gives you back a B. Now the caller has both A and B and both are still valid. Here we pass in an SGL and the SGL is transformed, so the caller only has B and A has been destroyed, i.e., the SGL can no longer be used as it was before, and there's no way to get A back. Maybe this is pointless bikeshedding, so if your color is the best, don't change anything. Bjorn
