vmscan: set up pagevec as late as possible in shrink_page_list()

shrink_page_list() sets up a pagevec to release pages as according as they
are free.  It uses significant amounts of stack on the pagevec.  This
patch adds pages to be freed via pagevec to a linked list which is then
freed en-masse at the end.  This avoids using stack in the main path that
potentially calls writepage().

Signed-off-by: Mel Gorman <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Michael Rubin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/vmscan.c

@@ -622,6 +622,24 @@ static enum page_references page_check_references(struct page *page,
 	return PAGEREF_RECLAIM;
 }
 
+static noinline_for_stack void free_page_list(struct list_head *free_pages)
+{
+	struct pagevec freed_pvec;
+	struct page *page, *tmp;
+
+	pagevec_init(&freed_pvec, 1);
+
+	list_for_each_entry_safe(page, tmp, free_pages, lru) {
+		list_del(&page->lru);
+		if (!pagevec_add(&freed_pvec, page)) {
+			__pagevec_free(&freed_pvec);
+			pagevec_reinit(&freed_pvec);
+		}
+	}
+
+	pagevec_free(&freed_pvec);
+}
+
 /*
  * shrink_page_list() returns the number of reclaimed pages
  */
@@ -630,13 +648,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 					enum pageout_io sync_writeback)
 {
 	LIST_HEAD(ret_pages);
-	struct pagevec freed_pvec;
+	LIST_HEAD(free_pages);
 	int pgactivate = 0;
 	unsigned long nr_reclaimed = 0;
 
 	cond_resched();
 
-	pagevec_init(&freed_pvec, 1);
 	while (!list_empty(page_list)) {
 		enum page_references references;
 		struct address_space *mapping;
@@ -811,10 +828,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		__clear_page_locked(page);
 free_it:
 		nr_reclaimed++;
-		if (!pagevec_add(&freed_pvec, page)) {
-			__pagevec_free(&freed_pvec);
-			pagevec_reinit(&freed_pvec);
-		}
+
+		/*
+		 * Is there need to periodically free_page_list? It would
+		 * appear not as the counts should be low
+		 */
+		list_add(&page->lru, &free_pages);
 		continue;
 
 cull_mlocked:
@@ -837,9 +856,10 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		list_add(&page->lru, &ret_pages);
 		VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
 	}
+
+	free_page_list(&free_pages);
+
 	list_splice(&ret_pages, page_list);
-	if (pagevec_count(&freed_pvec))
-		__pagevec_free(&freed_pvec);
 	count_vm_events(PGACTIVATE, pgactivate);
 	return nr_reclaimed;
 }