* [PATCH] mm: memcontrol: replace the loop with a list_for_each_entry()
@ 2021-02-04 10:53 Muchun Song
2021-02-04 15:14 ` Johannes Weiner
0 siblings, 1 reply; 3+ messages in thread
From: Muchun Song @ 2021-02-04 10:53 UTC (permalink / raw)
To: hannes, mhocko, vdavydov.dev, akpm
Cc: cgroups, linux-mm, linux-kernel, Muchun Song
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);
}
--
2.11.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] mm: memcontrol: replace the loop with a list_for_each_entry()
2021-02-04 10:53 [PATCH] mm: memcontrol: replace the loop with a list_for_each_entry() Muchun Song
@ 2021-02-04 15:14 ` Johannes Weiner
2021-02-04 15:55 ` [External] " Muchun Song
0 siblings, 1 reply; 3+ messages in thread
From: Johannes Weiner @ 2021-02-04 15:14 UTC (permalink / raw)
To: Muchun Song; +Cc: mhocko, vdavydov.dev, akpm, cgroups, linux-mm, linux-kernel
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [External] Re: [PATCH] mm: memcontrol: replace the loop with a list_for_each_entry()
2021-02-04 15:14 ` Johannes Weiner
@ 2021-02-04 15:55 ` Muchun Song
0 siblings, 0 replies; 3+ messages in thread
From: Muchun Song @ 2021-02-04 15:55 UTC (permalink / raw)
To: Johannes Weiner
Cc: Michal Hocko, Vladimir Davydov, Andrew Morton, Cgroups,
Linux Memory Management List, LKML
On Thu, Feb 4, 2021 at 11:14 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> 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()?
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
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-02-04 10:53 [PATCH] mm: memcontrol: replace the loop with a list_for_each_entry() Muchun Song
2021-02-04 15:14 ` Johannes Weiner
2021-02-04 15:55 ` [External] " Muchun Song
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