mm/swap.c: trivial mark_page_accessed() cleanup

This avoids duplicated PageReferenced() calls.  No behavior change.

Link: http://lkml.kernel.org/r/20191016225326.GB12497@wfg-t540p.sh.intel.com
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Liu Jingqi <jingqi.liu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swap.c

@@ -373,9 +373,16 @@ static void __lru_cache_activate_page(struct page *page)
 void mark_page_accessed(struct page *page)
 {
 	page = compound_head(page);
-	if (!PageActive(page) && !PageUnevictable(page) &&
-			PageReferenced(page)) {
 
+	if (!PageReferenced(page)) {
+		SetPageReferenced(page);
+	} else if (PageUnevictable(page)) {
+		/*
+		 * Unevictable pages are on the "LRU_UNEVICTABLE" list. But,
+		 * this list is never rotated or maintained, so marking an
+		 * evictable page accessed has no effect.
+		 */
+	} else if (!PageActive(page)) {
 		/*
 		 * If the page is on the LRU, queue it for activation via
 		 * activate_page_pvecs. Otherwise, assume the page is on a
@@ -389,8 +396,6 @@ void mark_page_accessed(struct page *page)
 		ClearPageReferenced(page);
 		if (page_is_file_cache(page))
 			workingset_activation(page);
-	} else if (!PageReferenced(page)) {
-		SetPageReferenced(page);
 	}
 	if (page_is_idle(page))
 		clear_page_idle(page);