linux-kernel - Re: [RFC PATCH 0/7] Make rstat flushing IRQ and sleep friendly

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Date:   Wed, 22 Mar 2023 21:10:21 -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 0/7] Make rstat flushing IRQ and sleep friendly

On Wed, Mar 22, 2023 at 9:00 PM Yosry Ahmed <yosryahmed@...gle.com> 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.