[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAJD7tkZJWXDinusUeYNBf_qov0+4ug2hG75Ge8NuP=6jG7+byA@mail.gmail.com>
Date: Wed, 22 Mar 2023 22:16:40 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Shakeel Butt <shakeelb@...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 9:32 PM Shakeel Butt <shakeelb@...gle.com> wrote:
>
> 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?
I believe through the charge/uncharge path we can do
memcg_check_events()->mem_cgroup_threshold()->mem_cgroup_usage()->mem_cgroup_flush_stats(),
right? I am assuming we can charge/uncharge memory in an interrupt
context.
Also the current code always disables interrupts before calling
memcg_check_events(), which made me suspect the percpu variables that
are modified by that call can also be modified in interrupt context.
>
> > 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