On Wed, Nov 23, 2016 at 9:27 AM, Bart Van Assche <bart.vanassche@xxxxxxxxxxx> wrote: > On 11/23/2016 09:13 AM, Logan Gunthorpe wrote: >> >> IMO any memory that has been registered for a P2P transaction should be >> locked from being evicted. So if there's a get_user_pages call it needs >> to be pinned until the put_page. The main issue being with the RDMA >> case: handling an eviction when a chunk of memory has been registered as >> an MR would be very tricky. The MR may be relied upon by another host >> and the kernel would have to inform user-space the MR was invalid then >> user-space would have to tell the remote application. > > > Hello Logan, > > Are you aware that the Linux kernel already supports ODP (On Demand Paging)? > See also the output of git grep -nHi on.demand.paging. See also > https://www.openfabrics.org/images/eventpresos/workshops2014/DevWorkshop/presos/Tuesday/pdf/04_ODP_update.pdf. > I don't think that was designed for the case where the backing memory is a special/static physical address range rather than anonymous "System RAM", right? I think we should handle the graphics P2P concerns separately from the general P2P-DMA case since the latter does not require the higher order memory management facilities. Using ZONE_DEVICE/DAX mappings to avoid changes to every driver that wants to support P2P-DMA separately from typical DMA still seems the path of least resistance. -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
