[PATCH 2/3] mm/vmscan: filter empty page_list at the beginning

[Wei Yang <richard.weiyang@gmail.com>]

node_page_list would always be !empty on finishing the loop, except
page_list is empty.

Let's handle empty page_list before doing any real work including
touching PF_MEMALLOC flag.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
---
 mm/vmscan.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9b5ce5778e9b..3a36ebd6295d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2533,9 +2533,12 @@ unsigned long reclaim_pages(struct list_head *page_list)
 		.no_demotion = 1,
 	};
 
+	if (list_empty(page_list))
+		return nr_reclaimed;
+
 	noreclaim_flag = memalloc_noreclaim_save();
 
-	while (!list_empty(page_list)) {
+	do {
 		page = lru_to_page(page_list);
 		if (nid == NUMA_NO_NODE) {
 			nid = page_to_nid(page);
@@ -2557,17 +2560,15 @@ unsigned long reclaim_pages(struct list_head *page_list)
 		}
 
 		nid = NUMA_NO_NODE;
-	}
+	} while (!list_empty(page_list));
 
-	if (!list_empty(&node_page_list)) {
-		nr_reclaimed += shrink_page_list(&node_page_list,
-						NODE_DATA(nid),
-						&sc, &dummy_stat, false);
-		while (!list_empty(&node_page_list)) {
-			page = lru_to_page(&node_page_list);
-			list_del(&page->lru);
-			putback_lru_page(page);
-		}
+	nr_reclaimed += shrink_page_list(&node_page_list,
+					NODE_DATA(nid),
+					&sc, &dummy_stat, false);
+	while (!list_empty(&node_page_list)) {
+		page = lru_to_page(&node_page_list);
+		list_del(&page->lru);
+		putback_lru_page(page);
 	}
 
 	memalloc_noreclaim_restore(noreclaim_flag);
-- 
2.33.1