On Thu, Aug 15, 2019 at 02:03:25PM -0400, Jerome Glisse wrote: > On Wed, Aug 14, 2019 at 07:48:28AM -0700, Dan Williams wrote: > > On Wed, Aug 14, 2019 at 6:28 AM Jason Gunthorpe <jgg@xxxxxxxxxxxx> wrote: > > > > > > On Wed, Aug 14, 2019 at 09:38:54AM +0200, Christoph Hellwig wrote: > > > > On Tue, Aug 13, 2019 at 06:36:33PM -0700, Dan Williams wrote: > > > > > Section alignment constraints somewhat save us here. The only example > > > > > I can think of a PMD not containing a uniform pgmap association for > > > > > each pte is the case when the pgmap overlaps normal dram, i.e. shares > > > > > the same 'struct memory_section' for a given span. Otherwise, distinct > > > > > pgmaps arrange to manage their own exclusive sections (and now > > > > > subsections as of v5.3). Otherwise the implementation could not > > > > > guarantee different mapping lifetimes. > > > > > > > > > > That said, this seems to want a better mechanism to determine "pfn is > > > > > ZONE_DEVICE". > > > > > > > > So I guess this patch is fine for now, and once you provide a better > > > > mechanism we can switch over to it? > > > > > > What about the version I sent to just get rid of all the strange > > > put_dev_pagemaps while scanning? Odds are good we will work with only > > > a single pagemap, so it makes some sense to cache it once we find it? > > > > Yes, if the scan is over a single pmd then caching it makes sense. > > Quite frankly an easier an better solution is to remove the pagemap > lookup as HMM user abide by mmu notifier it means we will not make > use or dereference the struct page so that we are safe from any > racing hotunplug of dax memory (as long as device driver using hmm > do not have a bug). Yes, I also would prefer to drop the confusing checks entirely - Christoph can you resend this patch? Thanks, Jason
