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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Marco Elver' <elver@google.com>
CC:     "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "glider@google.com" <glider@google.com>,
        "dvyukov@google.com" <dvyukov@google.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "kasan-dev@googlegroups.com" <kasan-dev@googlegroups.com>,
        Mel Gorman <mgorman@suse.de>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH] kfence: use TASK_IDLE when awaiting allocation
Thread-Topic: [PATCH] kfence: use TASK_IDLE when awaiting allocation
Thread-Index: AQHXThvT1D7AluRty02nSL8F2LU+eKrtrQGA///ysoCAABhIIA==
Date:   Fri, 21 May 2021 10:15:41 +0000
Message-ID: <4a93b6d6c82049fc83004104f3e76fd7@AcuMS.aculab.com>
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From: Marco Elver
> Sent: 21 May 2021 10:48
> 
> 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)

That's been added since I last tried to stop tasks updating
the load-average :-)

	David

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