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. ? Jason
