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/[email protected]/ Signed-off-by: Joao Martins <[email protected]> Reviewed-by: Dan Williams <[email protected]> --- drivers/dax/device.c | 57 ++++++++++++++++++++++++++++++++++---------- 1 file changed, 44 insertions(+), 13 deletions(-) diff --git a/drivers/dax/device.c b/drivers/dax/device.c index a65c67ab5ee0..0c2ac97d397d 100644 --- a/drivers/dax/device.c +++ b/drivers/dax/device.c @@ -192,6 +192,42 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax, } #endif /* !CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */ +static void set_page_mapping(struct vm_fault *vmf, pfn_t pfn, + unsigned long fault_size, + struct address_space *f_mapping) +{ + unsigned long i; + pgoff_t pgoff; + + pgoff = linear_page_index(vmf->vma, ALIGN(vmf->address, fault_size)); + + for (i = 0; i < fault_size / PAGE_SIZE; i++) { + struct page *page; + + page = pfn_to_page(pfn_t_to_pfn(pfn) + i); + if (page->mapping) + continue; + page->mapping = f_mapping; + page->index = pgoff + i; + } +} + +static void set_compound_mapping(struct vm_fault *vmf, pfn_t pfn, + unsigned long fault_size, + struct address_space *f_mapping) +{ + struct page *head; + + head = pfn_to_page(pfn_t_to_pfn(pfn)); + head = compound_head(head); + if (head->mapping) + return; + + head->mapping = f_mapping; + head->index = linear_page_index(vmf->vma, + ALIGN(vmf->address, fault_size)); +} + static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf, enum page_entry_size pe_size) { @@ -225,8 +261,7 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf, } if (rc == VM_FAULT_NOPAGE) { - unsigned long i; - pgoff_t pgoff; + struct dev_pagemap *pgmap = dev_dax->pgmap; /* * In the device-dax case the only possibility for a @@ -234,17 +269,10 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf, * mapped. No need to consider the zero page, or racing * conflicting mappings. */ - pgoff = linear_page_index(vmf->vma, - ALIGN(vmf->address, fault_size)); - for (i = 0; i < fault_size / PAGE_SIZE; i++) { - struct page *page; - - page = pfn_to_page(pfn_t_to_pfn(pfn) + i); - if (page->mapping) - continue; - page->mapping = filp->f_mapping; - page->index = pgoff + i; - } + if (pgmap->vmemmap_shift) + set_compound_mapping(vmf, pfn, fault_size, filp->f_mapping); + else + set_page_mapping(vmf, pfn, fault_size, filp->f_mapping); } dax_read_unlock(id); @@ -439,6 +467,9 @@ 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
