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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Wed, 22 Mar 2023 22:07:43 -0700
Message-ID: <CAJD7tkYYQjZyDpTc02WTGG_aW+wS8m2k407X3NhLrN8Y_5RKPA@mail.gmail.com>
Subject: Re: [RFC PATCH 0/7] Make rstat flushing IRQ and sleep friendly
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Tejun Heo <tj@kernel.org>, Josef Bacik <josef@toxicpanda.com>,
        Jens Axboe <axboe@kernel.dk>,
        Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Muchun Song <muchun.song@linux.dev>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vasily Averin <vasily.averin@linux.dev>,
        cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        bpf@vger.kernel.org
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On Wed, Mar 22, 2023 at 9:10=E2=80=AFPM Shakeel Butt <shakeelb@google.com> =
wrote:
>
> On Wed, Mar 22, 2023 at 9:00=E2=80=AFPM Yosry Ahmed <yosryahmed@google.co=
m> wrote:
> >
> > Currently, if rstat flushing is invoked using the irqsafe variant
> > cgroup_rstat_flush_irqsafe(), we keep interrupts disabled and do not
> > sleep for the entire flush operation, which is O(# cpus * # cgroups).
> > This can be rather dangerous.
> >
> > Not all contexts that use cgroup_rstat_flush_irqsafe() actually cannot
> > sleep, and among those that cannot sleep, not all contexts require
> > interrupts to be disabled.
>
> Too many negations in the above sentence is making it very confusing.

Sorry, this is indeed very confusing. I guess a better rephrasing is:

Multiple code paths use cgroup_rstat_flush_irqsafe(), but many of them
can sleep. Even among the code paths that actually cannot sleep,
multiple ones are interruptible.