linux-kernel - Re: [PATCH] kfence: use TASK_IDLE when awaiting allocation

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Date:   Fri, 21 May 2021 13:17:44 +0200
From:   Marco Elver <elver@...gle.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Mel Gorman <mgorman@...e.de>, stable <stable@...r.kernel.org>
Subject: Re: [PATCH] kfence: use TASK_IDLE when awaiting allocation

On Fri, 21 May 2021 at 11:37, Hillf Danton <hdanton@...a.com> wrote:
> On Fri, 21 May 2021 10:32:09 +0200 Marco Elver wrote:
> >Since wait_event() uses TASK_UNINTERRUPTIBLE by default, waiting for an
> >allocation counts towards load. However, for KFENCE, this does not make
> >any sense, since there is no busy work we're awaiting.
>
> Because of a blocking wq callback, kfence_timer should be queued on a
> unbound workqueue in the first place. Feel free to add a followup to
> replace system_power_efficient_wq with system_unbound_wq if it makes
> sense to you that kfence behaves as correctly as expected independent of
> CONFIG_WQ_POWER_EFFICIENT_DEFAULT given "system_power_efficient_wq is
> identical to system_wq if 'wq_power_efficient' is disabled."

Thanks for pointing it out -- I think this makes sense, let's just use
the unbound wq unconditionally. Since it's independent of this patch,
I've sent it separately:
https://lkml.kernel.org/r/20210521111630.472579-1-elver@google.com