On Wed, Jun 26, 2019 at 1:21 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote: > > On Wed, Jun 26, 2019 at 12:31:08PM -0600, Logan Gunthorpe wrote: > > > we have a hole behind len where we could store flag. Preferably > > > optionally based on a P2P or other magic memory types config > > > option so that 32-bit systems with 32-bit phys_addr_t actually > > > benefit from the smaller and better packing structure. > > > > That seems sensible. The one thing that's unclear though is how to get > > the PCI Bus address when appropriate. Can we pass that in instead of the > > phys_addr with an appropriate flag? Or will we need to pass the actual > > physical address and then, at the map step, the driver has to some how > > lookup the PCI device to figure out the bus offset? > > I agree with CH, if we go down this path it is a layering violation > for the thing injecting bio's into the block stack to know what struct > device they egress&dma map on just to be able to do the dma_map up > front. > > So we must be able to go from this new phys_addr_t&flags to some BAR > information during dma_map. > > For instance we could use a small hash table of the upper phys addr > bits, or an interval tree, to do the lookup. Hmm, that sounds like dev_pagemap without the pages. There's already no requirement that dev_pagemap point to real / present pages (DEVICE_PRIVATE) seems a straightforward extension to use it for helping coordinate phys_addr_t in 'struct bio'. Then Logan's future plans to let userspace coordinate p2p operations could build on PTE_DEVMAP.
