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.
BugLink: https://bugzilla.suse.com/show_bug.cgi?id=1185565
Fixes: 407f1d8c1b5f ("kfence: await for allocation using wait_event")
Signed-off-by: Marco Elver <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: <[email protected]> # v5.12+
---
mm/kfence/core.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index e18fbbd5d9b4..4d21ac44d5d3 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -627,10 +627,10 @@ static void toggle_allocation_gate(struct work_struct *work)
* During low activity with no allocations we might wait a
* while; let's avoid the hung task warning.
*/
- wait_event_timeout(allocation_wait, atomic_read(&kfence_allocation_gate),
- sysctl_hung_task_timeout_secs * HZ / 2);
+ wait_event_idle_timeout(allocation_wait, atomic_read(&kfence_allocation_gate),
+ sysctl_hung_task_timeout_secs * HZ / 2);
} else {
- wait_event(allocation_wait, atomic_read(&kfence_allocation_gate));
+ wait_event_idle(allocation_wait, atomic_read(&kfence_allocation_gate));
}
/* Disable static key and reset timer. */
--
2.31.1.818.g46aad6cb9e-goog
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.
IIRC the load-average is really intended to include processes
that are waiting for disk - especially for swap.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
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/[email protected]/T/
Thanks,
-- Marco
> IIRC the load-average is really intended to include processes
> that are waiting for disk - especially for swap.
>
> David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
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
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
On Fri, 21 May 2021 at 11:37, Hillf Danton <[email protected]> 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/[email protected]