mm: memcontrol: replace the loop with a list_for_each_entry()

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.

Link: https://lkml.kernel.org/r/20210204163055.56080-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ed5cc78a8dbfb28b65dc7ab9ef0a7e8fced558c8..8c035846c7a4c97a4be0ec88e97a4970c9c373a7 100644 (file)
--- 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);
 }
 
 /**