mm: accelerate mm_populate() treatment of THP pages

This change adds a follow_page_mask function which is equivalent to
follow_page, but with an extra page_mask argument.

follow_page_mask sets *page_mask to HPAGE_PMD_NR - 1 when it encounters
a THP page, and to 0 in other cases.

__get_user_pages() makes use of this in order to accelerate populating
THP ranges - that is, when both the pages and vmas arrays are NULL, we
don't need to iterate HPAGE_PMD_NR times to cover a single THP page (and
we also avoid taking mm->page_table_lock that many times).

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 2 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 87b0ef253607..6124f1db50fe 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1629,8 +1629,17 @@ int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
 int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
                         unsigned long pfn);
 
-struct page *follow_page(struct vm_area_struct *, unsigned long address,
-                        unsigned int foll_flags);
+struct page *follow_page_mask(struct vm_area_struct *vma,
+                              unsigned long address, unsigned int foll_flags,
+                              unsigned int *page_mask);
+
+static inline struct page *follow_page(struct vm_area_struct *vma,
+                unsigned long address, unsigned int foll_flags)
+{
+        unsigned int unused_page_mask;
+        return follow_page_mask(vma, address, foll_flags, &unused_page_mask);
+}
+
 #define FOLL_WRITE      0x01    /* check pte is writable */
 #define FOLL_TOUCH      0x02    /* mark page accessed */
 #define FOLL_GET        0x04    /* do get_page on page */