Commit e0975b2a authored Dec 28, 2018 by Michal Hocko Committed by Linus Torvalds Dec 28, 2018

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>

parent bb8965bd

mm/filemap.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -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;

Admin message