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 elver@google.com Cc: Mel Gorman mgorman@suse.de Cc: stable@vger.kernel.org # 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. */
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/alpine.LFD.2.11.1505112154420.1749@ja.home.ssi....
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)
Dear stable maintainers,
The patch "kfence: use TASK_IDLE when awaiting allocation" has landed in mainline as 8fd0e995cc7b, however, does not apply cleanly to 5.12.y due to a prerequisite patch missing.
My recommendation is to cherry-pick the following 2 commits to 5.12.y (rather than rebase 8fd0e995cc7b on top of 5.12.y):
37c9284f6932 kfence: maximize allocation wait timeout duration 8fd0e995cc7b kfence: use TASK_IDLE when awaiting allocation
Many thanks, -- Marco
---------- Forwarded message --------- From: Marco Elver elver@google.com Date: Fri, 21 May 2021 at 10:32 Subject: [PATCH] kfence: use TASK_IDLE when awaiting allocation To: elver@google.com, akpm@linux-foundation.org Cc: glider@google.com, dvyukov@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com, Mel Gorman mgorman@suse.de, stable@vger.kernel.org
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 elver@google.com Cc: Mel Gorman mgorman@suse.de Cc: stable@vger.kernel.org # v5.12+ --- mm/kfence/core.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
On Mon, Jun 07, 2021 at 04:23:34PM +0200, Marco Elver wrote:
Dear stable maintainers,
The patch "kfence: use TASK_IDLE when awaiting allocation" has landed in mainline as 8fd0e995cc7b, however, does not apply cleanly to 5.12.y due to a prerequisite patch missing.
My recommendation is to cherry-pick the following 2 commits to 5.12.y (rather than rebase 8fd0e995cc7b on top of 5.12.y):
37c9284f6932 kfence: maximize allocation wait timeout duration 8fd0e995cc7b kfence: use TASK_IDLE when awaiting allocation
Thanks, that worked!
greg k-h
linux-stable-mirror@lists.linaro.org
-
David Laight -
Greg Kroah-Hartman -
Marco Elver