2022-01-05 17:52:27

by Jann Horn

Subject: [PATCH] mm, oom: OOM sysrq should always kill a process

The OOM kill sysrq (alt+sysrq+F) should allow the user to kill the
process with the highest OOM badness with a single execution.

However, at the moment, the OOM kill can bail out if an OOM notifier
(e.g. the i915 one) says that it reclaimed a tiny amount of memory
from somewhere. That's probably not what the user wants.

As documented in struct oom_control, order == -1 means the oom kill is
required by sysrq. So check for that, and if it's true, don't bail out
no matter what the OOM notifiers say.

Signed-off-by: Jann Horn <[email protected]>
---
mm/oom_kill.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 1ddabefcfb5a..dc645cbc6e0d 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -1051,13 +1051,14 @@ EXPORT_SYMBOL_GPL(unregister_oom_notifier);
bool out_of_memory(struct oom_control *oc)
{
unsigned long freed = 0;
+ bool sysrq_forced = oc->order == -1;

if (oom_killer_disabled)
return false;

if (!is_memcg_oom(oc)) {
blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
- if (freed > 0)
+ if (freed > 0 && !sysrq_forced)
/* Got some memory back in the last second. */
return true;
}

base-commit: c9e6606c7fe92b50a02ce51dda82586ebdf99b48
--
2.34.1.448.ga2b2bfdf31-goog

2022-01-06 08:26:24

by Michal Hocko

Subject: Re: [PATCH] mm, oom: OOM sysrq should always kill a process

On Wed 05-01-22 18:51:15, Jann Horn wrote:
> The OOM kill sysrq (alt+sysrq+F) should allow the user to kill the
> process with the highest OOM badness with a single execution.
>
> However, at the moment, the OOM kill can bail out if an OOM notifier
> (e.g. the i915 one) says that it reclaimed a tiny amount of memory
> from somewhere. That's probably not what the user wants.
>
> As documented in struct oom_control, order == -1 means the oom kill is
> required by sysrq. So check for that, and if it's true, don't bail out
> no matter what the OOM notifiers say.

I agree that it is suboptimal to disable sysrq+f because of notfiers
because the OOM invocation is not a direct result of the OOM situation
but rather an admin will. We already kill a new task even if an oom
victim is still pending.

> Signed-off-by: Jann Horn <[email protected]>

with a minor update as below
Acked-by: Michal Hocko <[email protected]>

> ---
> mm/oom_kill.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 1ddabefcfb5a..dc645cbc6e0d 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -1051,13 +1051,14 @@ EXPORT_SYMBOL_GPL(unregister_oom_notifier);
> bool out_of_memory(struct oom_control *oc)
> {
> unsigned long freed = 0;
> + bool sysrq_forced = oc->order == -1;
>
> if (oom_killer_disabled)
> return false;
>
> if (!is_memcg_oom(oc)) {
> blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
> - if (freed > 0)
> + if (freed > 0 && !sysrq_forced)
> /* Got some memory back in the last second. */
> return true;
> }

is_sysrq_oom(oc) is a more appropriate way to check this.

>
> base-commit: c9e6606c7fe92b50a02ce51dda82586ebdf99b48
> --
> 2.34.1.448.ga2b2bfdf31-goog

--
Michal Hocko
SUSE Labs