[Fixup Vladimir email address]
On Mon 03-04-17 10:38:00, Michal Hocko wrote:
> On Sun 02-04-17 12:52:55, Tetsuo Handa wrote:
> > I noticed that SysRq-f prints
> >
> > "sysrq: OOM request ignored because killer is disabled"
> >
> > when no process was selected (rather than when oom killer was disabled).
> > This message was not printed until Linux 4.8 because commit 7c5f64f84483bd13
> > ("mm: oom: deduplicate victim selection code for memcg and global oom") changed
> > from "return true;" to "return !!oc->chosen;" when is_sysrq_oom(oc) is true.
> >
> > Is this what we meant?
> >
> > [ 713.805315] sysrq: SysRq : Manual OOM execution
> > [ 713.808920] Out of memory: Kill process 4468 ((agetty)) score 0 or sacrifice child
> > [ 713.814913] Killed process 4468 ((agetty)) total-vm:43704kB, anon-rss:1760kB, file-rss:0kB, shmem-rss:0kB
> > [ 714.004805] sysrq: SysRq : Manual OOM execution
> > [ 714.005936] Out of memory: Kill process 4469 (systemd-cgroups) score 0 or sacrifice child
> > [ 714.008117] Killed process 4469 (systemd-cgroups) total-vm:10704kB, anon-rss:120kB, file-rss:0kB, shmem-rss:0kB
> > [ 714.189310] sysrq: SysRq : Manual OOM execution
> > [ 714.193425] sysrq: OOM request ignored because killer is disabled
> > [ 714.381313] sysrq: SysRq : Manual OOM execution
> > [ 714.385158] sysrq: OOM request ignored because killer is disabled
> > [ 714.573320] sysrq: SysRq : Manual OOM execution
> > [ 714.576988] sysrq: OOM request ignored because killer is disabled
>
> So, what about this?
> ---
> From 6721932dba5b5143be0fa8110450231038af4238 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@xxxxxxxx>
> Date: Mon, 3 Apr 2017 10:30:14 +0200
> Subject: [PATCH] oom: improve oom disable handling
>
> Tetsuo has reported that sysrq triggered OOM killer will print a
> misleading information when no tasks are selected:
>
> [ 713.805315] sysrq: SysRq : Manual OOM execution
> [ 713.808920] Out of memory: Kill process 4468 ((agetty)) score 0 or sacrifice child
> [ 713.814913] Killed process 4468 ((agetty)) total-vm:43704kB, anon-rss:1760kB, file-rss:0kB, shmem-rss:0kB
> [ 714.004805] sysrq: SysRq : Manual OOM execution
> [ 714.005936] Out of memory: Kill process 4469 (systemd-cgroups) score 0 or sacrifice child
> [ 714.008117] Killed process 4469 (systemd-cgroups) total-vm:10704kB, anon-rss:120kB, file-rss:0kB, shmem-rss:0kB
> [ 714.189310] sysrq: SysRq : Manual OOM execution
> [ 714.193425] sysrq: OOM request ignored because killer is disabled
> [ 714.381313] sysrq: SysRq : Manual OOM execution
> [ 714.385158] sysrq: OOM request ignored because killer is disabled
> [ 714.573320] sysrq: SysRq : Manual OOM execution
> [ 714.576988] sysrq: OOM request ignored because killer is disabled
>
> The real reason is that there are no eligible tasks for the OOM killer
> to select but since 7c5f64f84483bd13 ("mm: oom: deduplicate victim
> selection code for memcg and global oom") the semantic of out_of_memory
> has changed without updating moom_callback.
>
> This patch updates moom_callback to tell that no task was eligible
> which is the case for both oom killer disabled and no eligible tasks.
> In order to help distinguish first case from the second add printk to
> both oom_killer_{enable,disable}. This information is useful on its own
> because it might help debugging potential memory allocation failures.
>
> Fixes: 7c5f64f84483bd13 ("mm: oom: deduplicate victim selection code for memcg and global oom")
> Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> drivers/tty/sysrq.c | 2 +-
> mm/oom_kill.c | 2 ++
> 2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index 71136742e606..a91f58dc2cb6 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -370,7 +370,7 @@ static void moom_callback(struct work_struct *ignored)
>
> mutex_lock(&oom_lock);
> if (!out_of_memory(&oc))
> - pr_info("OOM request ignored because killer is disabled\n");
> + pr_info("OOM request ignored. No task eligible\n");
> mutex_unlock(&oom_lock);
> }
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 51c091849dcb..ad2b112cdf3e 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -682,6 +682,7 @@ void exit_oom_victim(void)
> void oom_killer_enable(void)
> {
> oom_killer_disabled = false;
> + pr_info("OOM killer enabled.\n");
> }
>
> /**
> @@ -718,6 +719,7 @@ bool oom_killer_disable(signed long timeout)
> oom_killer_enable();
> return false;
> }
> + pr_info("OOM killer disabled.\n");
>
> return true;
> }
> --
> 2.11.0
>
>
> --
> Michal Hocko
> SUSE Labs
--
Michal Hocko
SUSE Labs
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