diff mbox series

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

Message ID 20181211142741.2607-4-mhocko@kernel.org (mailing list archive)
State New, archived
Headers show
Series few memory offlining enhancements | expand

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

Patch

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;