[PATCH v2] mm: memcontrol: replace the loop with a list_for_each_entry()

[Muchun Song <songmuchun@bytedance.com>]

The rule of list walk has gone since:

 commit a9d5adeeb4b2 ("mm/memcontrol: allow to uncharge page without using page->lru field")

So remove the strange comment and replace the loop with a
list_for_each_entry().

There is only one caller of the uncharge_list(). So just fold it into
mem_cgroup_uncharge_list() and remove it.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
v2:
 - Fold uncharge_list() to mem_cgroup_uncharge_list().

 mm/memcontrol.c | 35 ++++++++---------------------------
 1 file changed, 8 insertions(+), 27 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ed5cc78a8dbf..8c035846c7a4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6862,31 +6862,6 @@ static void uncharge_page(struct page *page, struct uncharge_gather *ug)
 	css_put(&ug->memcg->css);
 }
 
-static void uncharge_list(struct list_head *page_list)
-{
-	struct uncharge_gather ug;
-	struct list_head *next;
-
-	uncharge_gather_clear(&ug);
-
-	/*
-	 * Note that the list can be a single page->lru; hence the
-	 * do-while loop instead of a simple list_for_each_entry().
-	 */
-	next = page_list->next;
-	do {
-		struct page *page;
-
-		page = list_entry(next, struct page, lru);
-		next = page->lru.next;
-
-		uncharge_page(page, &ug);
-	} while (next != page_list);
-
-	if (ug.memcg)
-		uncharge_batch(&ug);
-}
-
 /**
  * mem_cgroup_uncharge - uncharge a page
  * @page: page to uncharge
@@ -6918,11 +6893,17 @@ void mem_cgroup_uncharge(struct page *page)
  */
 void mem_cgroup_uncharge_list(struct list_head *page_list)
 {
+	struct uncharge_gather ug;
+	struct page *page;
+
 	if (mem_cgroup_disabled())
 		return;
 
-	if (!list_empty(page_list))
-		uncharge_list(page_list);
+	uncharge_gather_clear(&ug);
+	list_for_each_entry(page, page_list, lru)
+		uncharge_page(page, &ug);
+	if (ug.memcg)
+		uncharge_batch(&ug);
 }
 
 /**
-- 
2.11.0