On Fri, Aug 16, 2019 at 5:24 AM Jason Gunthorpe <jgg@xxxxxxxxxxxx> wrote: > > On Thu, Aug 15, 2019 at 08:54:46PM -0700, Dan Williams wrote: > > > > However, this means we cannot do any processing of ZONE_DEVICE pages > > > outside the driver lock, so eg, doing any DMA map that might rely on > > > MEMORY_DEVICE_PCI_P2PDMA has to be done in the driver lock, which is > > > a bit unfortunate. > > > > Wouldn't P2PDMA use page pins? Not needing to hold a lock over > > ZONE_DEVICE page operations was one of the motivations for plumbing > > get_dev_pagemap() with a percpu-ref. > > hmm_range_fault() doesn't use page pins at all, so if a ZONE_DEVICE > page comes out of it then it needs to use another locking pattern. > > If I follow it all right: > > We can do a get_dev_pagemap inside the page_walk and touch the pgmap, > or we can do the 'device mutex && retry' pattern and touch the pgmap > in the driver, under that lock. > > However in all cases the current get_dev_pagemap()'s in the page walk > are not necessary, and we can delete them. Yes, as long as 'struct page' instances resulting from that lookup are not passed outside of that lock. _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
