On Thu, Feb 4, 2021 at 11:14 PM Johannes Weiner [off-list ref] wrote:

On Thu, Feb 04, 2021 at 06:53:20PM +0800, Muchun Song wrote:

quoted

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().

Signed-off-by: Muchun Song <redacted>
---
 mm/memcontrol.c | 17 ++---------------
 1 file changed, 2 insertions(+), 15 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6c7f1ea3955e..43341bd7ea1c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -6891,24 +6891,11 @@ static void uncharge_page(struct page *page, struct uncharge_gather *ug)
 static void uncharge_list(struct list_head *page_list)
 {
      struct uncharge_gather ug;
-     struct list_head *next;
+     struct page *page;

      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;
-
+     list_for_each_entry(page, page_list, lru)
              uncharge_page(page, &ug);
-     } while (next != page_list);
-
      uncharge_batch(&ug);

Good catch, this makes things much simpler.

Looking at the surrounding code, there also seems to be no reason
anymore to have uncharge_list() as a separate function: there is only
one caller after the mentioned commit, and it's trivial after your
change. Would you mind folding it into mem_cgroup_uncharge_list()?

Will do. Thanks.

The list_empty() check in that one is also unnecessary now: the
do-while loop required at least one page to be on the list or it would
crash, but list_for_each() will be just fine on an empty list.

Right. It makes things more simple.

Thanks