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SubjectRe: [PATCH] mm: memcontrol: replace the loop with a list_for_each_entry()
On Thu, Feb 04, 2021 at 06:53:20PM +0800, Muchun Song wrote:
> 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 <songmuchun@bytedance.com>
> ---
> 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()?

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.

Thanks

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