mm, fault_around: do not take a reference to a locked page

filemap_map_pages takes a speculative reference to each page in the range
before it tries to lock that page.  While this is correct it also can
influence page migration which will bail out when seeing an elevated
reference count.  The faultaround code would bail on seeing a locked page
so we can pro-actively check the PageLocked bit before
page_cache_get_speculative and prevent from pointless reference count
churn.

Link: http://lkml.kernel.org/r/20181211142741.2607-4-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Suggested-by: Jan Kara <jack@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index 8cec52968e834fb5c01bb7b81b162894ed389129..29655fb47a2c4b2cf61e1c61e5b06d6f51e537a8 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2614,6 +2614,13 @@ void filemap_map_pages(struct vm_fault *vmf,
                        goto next;
 
                head = compound_head(page);
+
+               /*
+                * Check for a locked page first, as a speculative
+                * reference may adversely influence page migration.
+                */
+               if (PageLocked(head))
+                       goto next;
                if (!page_cache_get_speculative(head))
                        goto next;