[3/3] mm, fault_around: do not take a reference to a locked page
diff mbox series

Message ID 20181211142741.2607-4-mhocko@kernel.org
State In Next
Commit ff1a544e1d0bea0e43372f8ba07c7b8198f18f10
Headers show
  • few memory offlining enhancements
Related show

Commit Message

Michal Hocko Dec. 11, 2018, 2:27 p.m. UTC
From: Michal Hocko <mhocko@suse.com>

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.

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>
Signed-off-by: Michal Hocko <mhocko@suse.com>
 mm/filemap.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff mbox series

diff --git a/mm/filemap.c b/mm/filemap.c
index 81adec8ee02c..a87f71fff879 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2553,6 +2553,13 @@  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;