Revert "mm: simplify code of swap.c"

This reverts commit d8505dee.

Chris Mason ended up chasing down some page allocation errors and pages
stuck waiting on the IO scheduler, and was able to narrow it down to two
commits: commit 744ed144 ("mm: batch activate_page() to reduce lock
contention") and d8505dee ("mm: simplify code of swap.c").

This reverts the second one.
Reported-and-debugged-by: Chris Mason <chris.mason@oracle.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <jaxboe@fusionio.com>
Cc: linux-mm <linux-mm@kvack.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swap.c

@@ -178,13 +178,15 @@ void put_pages_list(struct list_head *pages)
 }
 EXPORT_SYMBOL(put_pages_list);
 
-static void pagevec_lru_move_fn(struct pagevec *pvec,
-				void (*move_fn)(struct page *page, void *arg),
-				void *arg)
+/*
+ * pagevec_move_tail() must be called with IRQ disabled.
+ * Otherwise this may cause nasty races.
+ */
+static void pagevec_move_tail(struct pagevec *pvec)
 {
 	int i;
+	int pgmoved = 0;
 	struct zone *zone = NULL;
-	unsigned long flags = 0;
 
 	for (i = 0; i < pagevec_count(pvec); i++) {
 		struct page *page = pvec->pages[i];
@@ -192,41 +194,21 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,
 
 		if (pagezone != zone) {
 			if (zone)
-				spin_unlock_irqrestore(&zone->lru_lock, flags);
+				spin_unlock(&zone->lru_lock);
 			zone = pagezone;
-			spin_lock_irqsave(&zone->lru_lock, flags);
+			spin_lock(&zone->lru_lock);
 		}
-
-		(*move_fn)(page, arg);
-	}
-	if (zone)
-		spin_unlock_irqrestore(&zone->lru_lock, flags);
-	release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
-	pagevec_reinit(pvec);
-}
-
-static void pagevec_move_tail_fn(struct page *page, void *arg)
-{
-	int *pgmoved = arg;
-	struct zone *zone = page_zone(page);
-
 		if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
 			int lru = page_lru_base_type(page);
 			list_move_tail(&page->lru, &zone->lru[lru].list);
-		(*pgmoved)++;
+			pgmoved++;
 		}
-}
-
-/*
- * pagevec_move_tail() must be called with IRQ disabled.
- * Otherwise this may cause nasty races.
- */
-static void pagevec_move_tail(struct pagevec *pvec)
-{
-	int pgmoved = 0;
-
-	pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
+	}
+	if (zone)
+		spin_unlock(&zone->lru_lock);
 	__count_vm_events(PGROTATED, pgmoved);
+	release_pages(pvec->pages, pvec->nr, pvec->cold);
+	pagevec_reinit(pvec);
 }
 
 /*
@@ -534,33 +516,44 @@ void lru_add_page_tail(struct zone* zone,
 	}
 }
 
-static void ____pagevec_lru_add_fn(struct page *page, void *arg)
+/*
+ * Add the passed pages to the LRU, then drop the caller's refcount
+ * on them.  Reinitialises the caller's pagevec.
+ */
+void ____pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
 {
-	enum lru_list lru = (enum lru_list)arg;
-	struct zone *zone = page_zone(page);
-	int file = is_file_lru(lru);
-	int active = is_active_lru(lru);
+	int i;
+	struct zone *zone = NULL;
+
+	VM_BUG_ON(is_unevictable_lru(lru));
 
+	for (i = 0; i < pagevec_count(pvec); i++) {
+		struct page *page = pvec->pages[i];
+		struct zone *pagezone = page_zone(page);
+		int file;
+		int active;
+
+		if (pagezone != zone) {
+			if (zone)
+				spin_unlock_irq(&zone->lru_lock);
+			zone = pagezone;
+			spin_lock_irq(&zone->lru_lock);
+		}
 		VM_BUG_ON(PageActive(page));
 		VM_BUG_ON(PageUnevictable(page));
 		VM_BUG_ON(PageLRU(page));
-
 		SetPageLRU(page);
+		active = is_active_lru(lru);
+		file = is_file_lru(lru);
 		if (active)
 			SetPageActive(page);
 		update_page_reclaim_stat(zone, page, file, active);
 		add_page_to_lru_list(zone, page, lru);
-}
-
-/*
- * Add the passed pages to the LRU, then drop the caller's refcount
- * on them.  Reinitialises the caller's pagevec.
- */
-void ____pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
-{
-	VM_BUG_ON(is_unevictable_lru(lru));
-
-	pagevec_lru_move_fn(pvec, ____pagevec_lru_add_fn, (void *)lru);
+	}
+	if (zone)
+		spin_unlock_irq(&zone->lru_lock);
+	release_pages(pvec->pages, pvec->nr, pvec->cold);
+	pagevec_reinit(pvec);
 }
 
 EXPORT_SYMBOL(____pagevec_lru_add);