[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CALvZod5MnM8UJ0pj44QYb4sVwgFZ1B2KpSL6oqBQbJU3wH6eNA@mail.gmail.com>
Date: Wed, 22 Mar 2023 21:32:42 -0700
From: Shakeel Butt <shakeelb@...gle.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Tejun Heo <tj@...nel.org>, Josef Bacik <josef@...icpanda.com>,
Jens Axboe <axboe@...nel.dk>,
Zefan Li <lizefan.x@...edance.com>,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...nel.org>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Muchun Song <muchun.song@...ux.dev>,
Andrew Morton <akpm@...ux-foundation.org>,
Vasily Averin <vasily.averin@...ux.dev>,
cgroups@...r.kernel.org, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
bpf@...r.kernel.org
Subject: Re: [RFC PATCH 2/7] memcg: do not disable interrupts when holding stats_flush_lock
On Wed, Mar 22, 2023 at 9:00 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> The rstat flushing code was modified so that we do not disable interrupts
> when we hold the global rstat lock. Do the same for stats_flush_lock on
> the memcg side to avoid unnecessarily disabling interrupts throughout
> flushing.
>
> Since the code exclusively uses trylock to acquire this lock, it should
> be fine to hold from interrupt contexts or normal contexts without
> disabling interrupts as a deadlock cannot occur. For interrupt contexts
> we will return immediately without flushing anyway.
>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> ---
> mm/memcontrol.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5abffe6f8389..e0e92b38fa51 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -636,15 +636,17 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val)
>
> static void __mem_cgroup_flush_stats(void)
> {
> - unsigned long flag;
> -
> - if (!spin_trylock_irqsave(&stats_flush_lock, flag))
> + /*
> + * This lock can be acquired from interrupt context,
How? What's the code path?
> but we only acquire
> + * using trylock so it should be fine as we cannot cause a deadlock.
> + */
> + if (!spin_trylock(&stats_flush_lock))
> return;
>
> flush_next_time = jiffies_64 + 2*FLUSH_TIME;
> cgroup_rstat_flush_irqsafe(root_mem_cgroup->css.cgroup);
> atomic_set(&stats_flush_threshold, 0);
> - spin_unlock_irqrestore(&stats_flush_lock, flag);
> + spin_unlock(&stats_flush_lock);
> }
>
> void mem_cgroup_flush_stats(void)
> --
> 2.40.0.rc1.284.g88254d51c5-goog
>
Powered by blists - more mailing lists