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

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Date:   Fri, 21 May 2021 10:15:41 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Marco Elver' <elver@...gle.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

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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