On Tue, Jun 18, 2019 at 10:42 AM Nadav Amit <namit@xxxxxxxxxx> wrote: > > > On Jun 17, 2019, at 11:44 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > > > > On Wed, Jun 12, 2019 at 9:59 PM Nadav Amit <namit@xxxxxxxxxx> wrote: > >> Running some microbenchmarks on dax keeps showing find_next_iomem_res() > >> as a place in which significant amount of time is spent. It appears that > >> in order to determine the cacheability that is required for the PTE, > >> lookup_memtype() is called, and this one traverses the resources list in > >> an inefficient manner. This patch-set tries to improve this situation. > > > > Let's just do this lookup once per device, cache that, and replay it > > to modified vmf_insert_* routines that trust the caller to already > > know the pgprot_values. > > IIUC, one device can have multiple regions with different characteristics, > which require difference cachability. Not for pmem. It will always be one common cacheability setting for the entirety of persistent memory. > Apparently, that is the reason there > is a tree of resources. Please be more specific about where you want to > cache it, please. The reason for lookup_memtype() was to try to prevent mixed cacheability settings of pages across different processes . The mapping type for pmem/dax is established by one of: drivers/nvdimm/pmem.c:413: addr = devm_memremap_pages(dev, &pmem->pgmap); drivers/nvdimm/pmem.c:425: addr = devm_memremap_pages(dev, &pmem->pgmap); drivers/nvdimm/pmem.c:432: addr = devm_memremap(dev, pmem->phys_addr, drivers/nvdimm/pmem.c-433- pmem->size, ARCH_MEMREMAP_PMEM); ...and is constant for the life of the device and all subsequent mappings. > Perhaps you want to cache the cachability-mode in vma->vm_page_prot (which I > see being done in quite a few cases), but I don’t know the code well enough > to be certain that every vma should have a single protection and that it > should not change afterwards. No, I'm thinking this would naturally fit as a property hanging off a 'struct dax_device', and then create a version of vmf_insert_mixed() and vmf_insert_pfn_pmd() that bypass track_pfn_insert() to insert that saved value.
