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

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Date:   Fri, 21 May 2021 11:47:41 +0200
From:   Marco Elver <elver@...gle.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "glider@...gle.com" <glider@...gle.com>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        Mel Gorman <mgorman@...e.de>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] kfence: use TASK_IDLE when awaiting allocation

On Fri, May 21, 2021 at 09:39AM +0000, David Laight wrote:
> From: Marco Elver
> > Sent: 21 May 2021 09:32
> > 
> > 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.
> > 
> > Instead, use TASK_IDLE via wait_event_idle() to not count towards load.
> 
> Doesn't that let the process be interruptible by a signal.
> Which is probably not desirable.
> 
> There really ought to be a way of sleeping with TASK_UNINTERRUPTIBLE
> without changing the load-average.

That's what TASK_IDLE is:

	include/linux/sched.h:#define TASK_IDLE                 (TASK_UNINTERRUPTIBLE | TASK_NOLOAD)

See https://lore.kernel.org/lkml/alpine.LFD.2.11.1505112154420.1749@ja.home.ssi.bg/T/

Thanks,
-- Marco

> IIRC the load-average is really intended to include processes
> that are waiting for disk - especially for swap.
> 
> 	David
> 
> -
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