[patch]vmscan: protect exectuable page from inactive list scan

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With commit 645747462435, pte referenced file page isn't activated in inactive
list scan. For VM_EXEC page, if it can't get a chance to active list, the
executable page protect loses its effect. We protect such page in inactive scan
here, now such page will be guaranteed cached in a full scan of active and
inactive list, which restores previous behavior.

Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index c5dfabf..b973048 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -608,8 +608,15 @@ static enum page_references page_check_references(struct page *page,
 		 * quickly recovered.
 		 */
 		SetPageReferenced(page);
-
-		if (referenced_page)
+		/*
+		 * Identify pte referenced and file-backed pages and give them
+		 * one trip around the active list. So that executable code get
+		 * better chances to stay in memory under moderate memory
+		 * pressure. JVM can create lots of anon VM_EXEC pages, so we
+		 * ignore them here.
+		 */
+		if (referenced_page || ((vm_flags & VM_EXEC) &&
+		    page_is_file_cache(page)))
 			return PAGEREF_ACTIVATE;
 
 		return PAGEREF_KEEP;


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