mm: munlock: manual pte walk in fast path instead of follow_page_mask()

Currently munlock_vma_pages_range() calls follow_page_mask() to obtain
each individual struct page.  This entails repeated full page table
translations and page table lock taken for each page separately.

This patch avoids the costly follow_page_mask() where possible, by
iterating over ptes within single pmd under single page table lock.  The
first pte is obtained by get_locked_pte() for non-THP page acquired by the
initial follow_page_mask().  The rest of the on-stack pagevec for munlock
is filled up using pte_walk as long as pte_present() and vm_normal_page()
are sufficient to obtain the struct page.

After this patch, a 14% speedup was measured for munlocking a 56GB large
memory area with THP disabled.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jörn Engel <joern@logfs.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michel Lespinasse <walken@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 6 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index dce24569f8fc..03f84b8d7359 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -643,12 +643,12 @@ static inline enum zone_type page_zonenum(const struct page *page)
 #endif
 
 /*
- * The identification function is only used by the buddy allocator for
- * determining if two pages could be buddies. We are not really
- * identifying a zone since we could be using a the section number
- * id if we have not node id available in page flags.
- * We guarantee only that it will return the same value for two
- * combinable pages in a zone.
+ * The identification function is mainly used by the buddy allocator for
+ * determining if two pages could be buddies. We are not really identifying
+ * the zone since we could be using the section number id if we do not have
+ * node id available in page flags.
+ * We only guarantee that it will return the same value for two combinable
+ * pages in a zone.
  */
 static inline int page_zone_id(struct page *page)
 {