Re: [PATCH 2/5] mm, memcg: narrow the scope of percpu_charge_mutex

Michal Hocko
2021-08-03T07:11:25Z

On Tue 03-08-21 14:29:13, Miaohe Lin wrote:
[...]
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 616d1a72ece3..6210b1124929 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2208,11 +2208,11 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
> */
> static void drain_all_stock(struct mem_cgroup *root_memcg)
> {
> - static DEFINE_MUTEX(percpu_charge_mutex);
> int cpu, curcpu;
> + static atomic_t drainer = ATOMIC_INIT(0);
>
> /* If someone's already draining, avoid adding running more workers. */
> - if (!mutex_trylock(&percpu_charge_mutex))
> + if (atomic_cmpxchg(&drainer, 0, 1) != 0)
> return;
> /*
> * Notify other cpus that system-wide "drain" is running
> @@ -2244,7 +2244,7 @@ static void drain_all_stock(struct mem_cgroup *root_memcg)
> }
> }
> put_cpu();
> - mutex_unlock(&percpu_charge_mutex);
> + atomic_set(&drainer, 0);

atomic_set doesn't imply memory barrier IIRC. Is this safe?

--
Michal Hocko
SUSE Labs