Re: [PATCH 1/2] mm: add sysctl to control global OOM logging behaviour

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On Wed 08-11-17 09:18:42, Dmitry Monakhov wrote:
> Our systems becomes bigger and bigger, but OOM still happens.
> This becomes serious problem for systems where OOM happens
> frequently(containers, VM) because each OOM generate pressure
> on dmesg log infrastructure. Let's allow system administrator
> ability to tune OOM dump behaviour
> 
> Disable oom log dump globaly:
> # echo 0 > /proc/sys/vm/oom_dump_log
> Enable oom log dump globaly:
> # echo 1 > /proc/sys/vm/oom_dump_log

We already do have sysctl_oom_dump_tasks to silence a potentially
lengthy task list output. show_mem is using a default print level
but I can imagine we can make it pr_info. Would that be sufficient?
I have to confess I am not really happy yet another tunable to control
the output. The same applies to the memcg case in the other email.
 
> Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
> ---
>  Documentation/sysctl/vm.txt | 13 +++++++++++++
>  include/linux/oom.h         |  1 +
>  kernel/sysctl.c             |  7 +++++++
>  mm/oom_kill.c               | 40 ++++++++++++++++++++++------------------
>  4 files changed, 43 insertions(+), 18 deletions(-)
> 
> diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
> index 9baf66a..09d69a0 100644
> --- a/Documentation/sysctl/vm.txt
> +++ b/Documentation/sysctl/vm.txt
> @@ -617,7 +617,20 @@ Default order is recommended unless this is causing problems for your
>  system/application.
>  
>  ==============================================================
> +oom_dump_log
>  
> +Enables a system-wide dump to be produced when the kernel performs an
> +OOM-killing. This sysctl control dump about  general information of OOM state
> +
> +If this is set to zero, this information is suppressed.  On very
> +large systems with thousands of tasks it may not be feasible to dump
> +the memory state information for each OOM event.  Such systems should
> +not be forced to incur a performance penalty in OOM conditions when the
> +information may not be desired.
> +
> +The default value is 1 (enabled).
> +
> +==============================================================
>  oom_dump_tasks
>  
>  Enables a system-wide task dump (excluding kernel threads) to be produced
> diff --git a/include/linux/oom.h b/include/linux/oom.h
> index 01c91d8..8ff56d3 100644
> --- a/include/linux/oom.h
> +++ b/include/linux/oom.h
> @@ -104,6 +104,7 @@ extern unsigned long oom_badness(struct task_struct *p,
>  
>  /* sysctls */
>  extern int sysctl_oom_dump_tasks;
> +extern int sysctl_oom_dump_log;
>  extern int sysctl_oom_kill_allocating_task;
>  extern int sysctl_panic_on_oom;
>  #endif /* _INCLUDE_LINUX_OOM_H */
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index d9c31bc..87163c1 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1263,6 +1263,13 @@ static int sysrq_sysctl_handler(struct ctl_table *table, int write,
>  		.proc_handler	= proc_dointvec,
>  	},
>  	{
> +		.procname	= "oom_dump_log",
> +		.data		= &sysctl_oom_dump_log,
> +		.maxlen		= sizeof(sysctl_oom_dump_log),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec,
> +	},
> +	{
>  		.procname	= "overcommit_ratio",
>  		.data		= &sysctl_overcommit_ratio,
>  		.maxlen		= sizeof(sysctl_overcommit_ratio),
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index dee0f75..02c8f5d6 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -51,6 +51,7 @@
>  int sysctl_panic_on_oom;
>  int sysctl_oom_kill_allocating_task;
>  int sysctl_oom_dump_tasks = 1;
> +int sysctl_oom_dump_log = 1;
>  
>  DEFINE_MUTEX(oom_lock);
>  
> @@ -552,7 +553,8 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
>  					 NULL);
>  	}
>  	tlb_finish_mmu(&tlb, 0, -1);
> -	pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
> +	if (sysctl_oom_dump_log)
> +		pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
>  			task_pid_nr(tsk), tsk->comm,
>  			K(get_mm_counter(mm, MM_ANONPAGES)),
>  			K(get_mm_counter(mm, MM_FILEPAGES)),
> @@ -578,11 +580,11 @@ static void oom_reap_task(struct task_struct *tsk)
>  	if (attempts <= MAX_OOM_REAP_RETRIES)
>  		goto done;
>  
> -
> -	pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
> -		task_pid_nr(tsk), tsk->comm);
> -	debug_show_all_locks();
> -
> +	if (sysctl_oom_dump_log) {
> +		pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
> +			task_pid_nr(tsk), tsk->comm);
> +		debug_show_all_locks();
> +	}
>  done:
>  	tsk->oom_reaper_list = NULL;
>  
> @@ -647,7 +649,7 @@ static int __init oom_init(void)
>  }
>  subsys_initcall(oom_init)
>  #else
> -static inline void wake_oom_reaper(struct task_struct *tsk)
> +static inline void wake_oom_reaper(struct task_struct *tsk, bool verbose)
>  {
>  }
>  #endif /* CONFIG_MMU */
> @@ -847,13 +849,13 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
>  		return;
>  	}
>  	task_unlock(p);
> +	if (sysctl_oom_dump_log) {
> +		if (__ratelimit(&oom_rs))
> +			dump_header(oc, p);
>  
> -	if (__ratelimit(&oom_rs))
> -		dump_header(oc, p);
> -
> -	pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n",
> -		message, task_pid_nr(p), p->comm, points);
> -
> +		pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n",
> +		       message, task_pid_nr(p), p->comm, points);
> +	}
>  	/*
>  	 * If any of p's children has a different mm and is eligible for kill,
>  	 * the one with the highest oom_badness() score is sacrificed for its
> @@ -907,11 +909,13 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
>  	 */
>  	do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
>  	mark_oom_victim(victim);
> -	pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
> -		task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
> -		K(get_mm_counter(victim->mm, MM_ANONPAGES)),
> -		K(get_mm_counter(victim->mm, MM_FILEPAGES)),
> -		K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
> +	if (sysctl_oom_dump_log)
> +		pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
> +		       task_pid_nr(victim), victim->comm,
> +		       K(victim->mm->total_vm),
> +		       K(get_mm_counter(victim->mm, MM_ANONPAGES)),
> +		       K(get_mm_counter(victim->mm, MM_FILEPAGES)),
> +		       K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
>  	task_unlock(victim);
>  
>  	/*
> -- 
> 1.8.3.1
> 
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-- 
Michal Hocko
SUSE Labs
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