vmscan: activate executable pages after first usage

commit c909e993 upstream.

Stable note: Not tracked in Bugzilla. There were reports of shared
	mapped pages being unfairly reclaimed in comparison to older kernels.
	This is being addressed over time.

Logic added in commit 8cab4754 ("vmscan: make mapped executable pages
the first class citizen") was noticeably weakened in commit
64574746 ("vmscan: detect mapped file pages used only once").

Currently these pages can become "first class citizens" only after second
usage.  After this patch page_check_references() will activate they after
first usage, and executable code gets yet better chance to stay in memory.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Shaohua Li <shaohua.li@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

mm/vmscan.c

@@ -718,6 +718,12 @@ static enum page_references page_check_references(struct page *page,
 		if (referenced_page || referenced_ptes > 1)
 			return PAGEREF_ACTIVATE;
 
+		/*
+		 * Activate file-backed executable pages after first usage.
+		 */
+		if (vm_flags & VM_EXEC)
+			return PAGEREF_ACTIVATE;
+
 		return PAGEREF_KEEP;
 	}