Re: [PATCH 1/3] mm: pagevec: Defer deciding what LRU to add a page to until pagevec drain time

On Fri, May 03, 2013 at 09:51:58AM +0200, Jan Kara wrote:

quoted

@@ -789,17 +787,16 @@ void lru_add_page_tail(struct page *page, struct page *page_tail,
 static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
 				 void *arg)
 {
-	enum lru_list lru = (enum lru_list)arg;
-	int file = is_file_lru(lru);
-	int active = is_active_lru(lru);
+	enum lru_list requested_lru = (enum lru_list)arg;
+	int file = page_is_file_cache(page);
+	int active = PageActive(page);
+	enum lru_list lru = page_lru(page);
 
-	VM_BUG_ON(PageActive(page));
+	WARN_ON_ONCE(requested_lru < NR_LRU_LISTS && requested_lru != lru);

  Hum, so __lru_cache_add() calls this with 'requested_lru' set to whatever
LRU we currently want to add a page. How should this always be equal to the
LRU of all the pages we have cached in the pagevec?

It wouldn't necessarily be and and for a pagevec drain, it's ignored
completely.

And if I'm right, there doesn't seem to be a reason to pass requested_lru
to this function at all, does it?

You've already noticed that it gets thrown away later in the third
patch. It was left in this patch as a debugging aid in case there was a
direct pagevec user that expected to place pages on an LRU that was at
odds with the page flags.

-- 
Mel Gorman
SUSE Labs

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