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SubjectRe: [PATCH] mm: memcontrol: fix missing wakeup polling thread
On Wed, Nov 04, 2020 at 08:55:58PM +0800, Muchun Song wrote:
> When wen poll the memory.swap.events, we can miss being waked up when the
> swap event occurs. Because we didn't notify.
>
> Fixes: f3a53a3a1e5b ("mm, memcontrol: implement memory.swap.events")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Good catch!

> ---
> include/linux/memcontrol.h | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 0f4dd7829fb2..2456cb737329 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1071,15 +1071,29 @@ static inline void count_memcg_event_mm(struct mm_struct *mm,
> rcu_read_unlock();
> }
>
> +static inline bool is_swap_memory_event(enum memcg_memory_event event)
> +{
> + return event == MEMCG_SWAP_HIGH || event == MEMCG_SWAP_MAX ||
> + event == MEMCG_SWAP_FAIL;
> +}

Please inline this, it's not really worth the indirection.

> static inline void memcg_memory_event(struct mem_cgroup *memcg,
> enum memcg_memory_event event)
> {
> + bool swap_event = is_swap_memory_event(event);
> + struct cgroup_file *cfile;
> +
> atomic_long_inc(&memcg->memory_events_local[event]);
> - cgroup_file_notify(&memcg->events_local_file);
> + if (swap_event) {
> + cfile = &memcg->swap_events_file;
> + } else {
> + cfile = &memcg->events_file;
> + cgroup_file_notify(&memcg->events_local_file);
> + }
>
> do {
> atomic_long_inc(&memcg->memory_events[event]);
> - cgroup_file_notify(&memcg->events_file);
> + cgroup_file_notify(cfile);

This loop is a walk up the hierarchy and memcg keeps changing, so you
cannot cache cfile up front.

if (swap_event)
cgroup_file_notify(&memcg->swap_events_file);
else
cgroup_file_notify(&memcg->events_file);

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