Use the newly added compound devmap facility which maps the assigned dax ranges as compound pages at a page size of @align.
dax devices are created with a fixed @align (huge page size) which is enforced through as well at mmap() of the device. Faults, consequently happen too at the specified @align specified at the creation, and those don't change throughout dax device lifetime. MCEs unmap a whole dax huge page, as well as splits occurring at the configured page size. Performance measured by gup_test improves considerably for unpin_user_pages() and altmap with NVDIMMs: $ gup_test -f /dev/dax1.0 -m 16384 -r 10 -S -a -n 512 -w (pin_user_pages_fast 2M pages) put:~71 ms -> put:~22 ms [altmap] (pin_user_pages_fast 2M pages) get:~524ms put:~525 ms -> get: ~127ms put:~71ms $ gup_test -f /dev/dax1.0 -m 129022 -r 10 -S -a -n 512 -w (pin_user_pages_fast 2M pages) put:~513 ms -> put:~188 ms [altmap with -m 127004] (pin_user_pages_fast 2M pages) get:~4.1 secs put:~4.12 secs -> get:~1sec put:~563ms .. as well as unpin_user_page_range_dirty_lock() being just as effective as THP/hugetlb[0] pages. [0] https://lore.kernel.org/linux-mm/20210212130843.13865-5-joao.m.mart...@oracle.com/ Signed-off-by: Joao Martins <joao.m.mart...@oracle.com> Reviewed-by: Dan Williams <dan.j.willi...@intel.com> --- drivers/dax/device.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/dax/device.c b/drivers/dax/device.c index 914368164e05..6ef8f374e27b 100644 --- a/drivers/dax/device.c +++ b/drivers/dax/device.c @@ -78,14 +78,20 @@ static void dax_set_mapping(struct vm_fault *vmf, pfn_t pfn, { unsigned long i, nr_pages = fault_size / PAGE_SIZE; struct file *filp = vmf->vma->vm_file; + struct dev_dax *dev_dax = filp->private_data; pgoff_t pgoff; + /* mapping is only set on the head */ + if (dev_dax->pgmap->vmemmap_shift) + nr_pages = 1; + pgoff = linear_page_index(vmf->vma, ALIGN(vmf->address, fault_size)); for (i = 0; i < nr_pages; i++) { struct page *page = pfn_to_page(pfn_t_to_pfn(pfn) + i); + page = compound_head(page); if (page->mapping) continue; @@ -443,6 +449,9 @@ int dev_dax_probe(struct dev_dax *dev_dax) } pgmap->type = MEMORY_DEVICE_GENERIC; + if (dev_dax->align > PAGE_SIZE) + pgmap->vmemmap_shift = + order_base_2(dev_dax->align >> PAGE_SHIFT); addr = devm_memremap_pages(dev, pgmap); if (IS_ERR(addr)) return PTR_ERR(addr); -- 2.17.2
