2021-03-30 10:22:44

by Muchun Song

Subject: [RFC PATCH 01/15] mm: memcontrol: fix page charging in page replacement

The pages aren't accounted at the root level, so do not charge the page
to the root memcg in page replacement. Although we do not display the
value (mem_cgroup_usage) so there shouldn't be any actual problem, but
there is a WARN_ON_ONCE in the page_counter_cancel(). Who knows if it
will trigger? So it is better to fix it.

Signed-off-by: Muchun Song <[email protected]>
---
mm/memcontrol.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 249bf6b4d94c..d0c4f6e91e17 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6936,9 +6936,11 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage)
/* Force-charge the new page. The old one will be freed soon */
nr_pages = thp_nr_pages(newpage);

- page_counter_charge(&memcg->memory, nr_pages);
- if (do_memsw_account())
- page_counter_charge(&memcg->memsw, nr_pages);
+ if (!mem_cgroup_is_root(memcg)) {
+ page_counter_charge(&memcg->memory, nr_pages);
+ if (do_memsw_account())
+ page_counter_charge(&memcg->memsw, nr_pages);
+ }

css_get(&memcg->css);
commit_charge(newpage, memcg);
--
2.11.0

2021-04-02 15:08:43

by Johannes Weiner

Subject: Re: [RFC PATCH 01/15] mm: memcontrol: fix page charging in page replacement

On Tue, Mar 30, 2021 at 06:15:17PM +0800, Muchun Song wrote:
> The pages aren't accounted at the root level, so do not charge the page
> to the root memcg in page replacement. Although we do not display the
> value (mem_cgroup_usage) so there shouldn't be any actual problem, but
> there is a WARN_ON_ONCE in the page_counter_cancel(). Who knows if it
> will trigger? So it is better to fix it.
>
> Signed-off-by: Muchun Song <[email protected]>

Acked-by: Johannes Weiner <[email protected]>