mm/gup: cache dev_pagemap while pinning pages
Getting pages from ZONE_DEVICE memory needs to check the backing device's
live-ness, which is tracked in the device's dev_pagemap metadata. This
metadata is stored in a radix tree and looking it up adds measurable
software overhead.
This patch avoids repeating this relatively costly operation when
dev_pagemap is used by caching the last dev_pagemap while getting user
pages. The gup_benchmark kernel self test reports this reduces time to
get user pages to as low as 1/3 of the previous time.
Link: http://lkml.kernel.org/r/20181012173040.15669-1-keith.busch@intel.com
Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8ea1b36..25c7d75 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -852,11 +852,10 @@ static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
}
struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
- pmd_t *pmd, int flags)
+ pmd_t *pmd, int flags, struct dev_pagemap **pgmap)
{
unsigned long pfn = pmd_pfn(*pmd);
struct mm_struct *mm = vma->vm_mm;
- struct dev_pagemap *pgmap;
struct page *page;
assert_spin_locked(pmd_lockptr(mm, pmd));
@@ -886,12 +885,11 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
return ERR_PTR(-EEXIST);
pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
- pgmap = get_dev_pagemap(pfn, NULL);
- if (!pgmap)
+ *pgmap = get_dev_pagemap(pfn, *pgmap);
+ if (!*pgmap)
return ERR_PTR(-EFAULT);
page = pfn_to_page(pfn);
get_page(page);
- put_dev_pagemap(pgmap);
return page;
}
@@ -1000,11 +998,10 @@ static void touch_pud(struct vm_area_struct *vma, unsigned long addr,
}
struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
- pud_t *pud, int flags)
+ pud_t *pud, int flags, struct dev_pagemap **pgmap)
{
unsigned long pfn = pud_pfn(*pud);
struct mm_struct *mm = vma->vm_mm;
- struct dev_pagemap *pgmap;
struct page *page;
assert_spin_locked(pud_lockptr(mm, pud));
@@ -1028,12 +1025,11 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
return ERR_PTR(-EEXIST);
pfn += (addr & ~PUD_MASK) >> PAGE_SHIFT;
- pgmap = get_dev_pagemap(pfn, NULL);
- if (!pgmap)
+ *pgmap = get_dev_pagemap(pfn, *pgmap);
+ if (!*pgmap)
return ERR_PTR(-EFAULT);
page = pfn_to_page(pfn);
get_page(page);
- put_dev_pagemap(pgmap);
return page;
}
