reduce swap due to shrink_mmap failures

@@ -301,7 +301,7 @@
  */
 int shrink_mmap(int priority, int gfp_mask)
 {
-	int ret = 0, count, nr_dirty;
+	int ret = 0, count, nr_dirty, scan = 0;
 	struct list_head * page_lru;
 	struct page * page = NULL;
 	

@@ -310,20 +310,44 @@
 
 	/* we need pagemap_lru_lock for list_del() ... subtle code below */
 	spin_lock(&pagemap_lru_lock);
-	while (count > 0 && (page_lru = lru_cache.prev) != &lru_cache) {
+	page_lru = &lru_cache;
+	while (count > 0) {
+                page_lru = page_lru->prev;
+                if (page_lru == &lru_cache) {
+		  /* one whole run, ALL lru pages aged */
+		  scan++;
+		  if (scan < 2)
+		    continue;
+		  else
+		    /* a) no freeable pages in LRU
+		     * b) no zone with preasure
+		     */
+		    break;
+		}
+
 		page = list_entry(page_lru, struct page, lru);
-		list_del(page_lru);
 
 		if (PageTestandClearReferenced(page)) {
 			page->age += PG_AGE_ADV;
 			if (page->age > PG_AGE_MAX)
 				page->age = PG_AGE_MAX;
-			goto dispose_continue;
+			continue;
 		}
+
+		/*
+		 * Page is from a zone we don't care about.
+		 * Don't drop page cache entries in vain.
+		 * Note: placement allows pages to gain age during
+		 * fast scan, but not loose - avoids all pages
+		 * becoming zero.
+		 */
+		if (page->zone->free_pages > page->zone->pages_high)
+			continue;
+
 		page->age -= min(PG_AGE_DECL, page->age);
 
 		if (page->age)
-			goto dispose_continue;
+			continue;
 
 		count--;
 		/*

@@ -331,10 +355,34 @@
 		 * immediate tell are untouchable..
 		 */
 		if (!page->buffers && page_count(page) > 1)
-			goto dispose_continue;
+			continue;
 
 		if (TryLockPage(page))
-			goto dispose_continue;
+			continue;
+
+		/* Move header before unlock...
+		 * NOTE: the page to scan might move on while having
+		 * pagemap_lru unlocked. Avoid rescanning pages
+		 * by moving head and removing current.
+		 */
+
+		/*
+		 * Equivalent code follows
+		 *
+		 *   list_del(&lru_cache);
+		 *   list_add_tail(&lru_cache, page_lru);
+		 *   list_del(page_lru);
+		 */
+		if (lru_cache.prev == page_lru) {
+		  /* Handle case with only one page on lru...
+		   * also optimize if first page checked is suitable.
+		   */
+		  list_del(page_lru);
+		}
+		else {
+		  list_del(&lru_cache);
+		  __list_add(&lru_cache, page_lru->prev, page_lru->next);
+		}
 
 		/* Release the pagemap_lru lock even if the page is not yet
 		   queued in any lru queue since we have just locked down

@@ -361,13 +409,6 @@
 			}
 		}
 
-		/*
-		 * Page is from a zone we don't care about.
-		 * Don't drop page cache entries in vain.
-		 */
-		if (page->zone->free_pages > page->zone->pages_high)
-			goto unlock_continue;
-
 		/* Take the pagecache_lock spinlock held to avoid
 		   other tasks to notice the page while we are looking at its
 		   page count. If it's a pagecache-page we'll free it

@@ -424,7 +465,11 @@
 		UnlockPage(page);
 		page_cache_release(page);
 dispose_continue:
+		/* page_lru was deleted from list. Reinsert it at _new_
+		 * lru_cache location
+		 */
 		list_add(page_lru, &lru_cache);
+		page_lru =  &lru_cache;
 	}
 	goto out;
 

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