Re: [RFC PATCH] mm/oom_kill: show oom eligibility when displaying the current memory state of all tasks

[Waiman Long <llong@redhat.com>]

On 6/11/21 1:19 PM, Aaron Tomlin wrote:
> At the present time, when showing potential OOM victims, we do not
> exclude tasks which already have MMF_OOM_SKIP set; it is possible that
> the last OOM killable victim was already OOM killed, yet the OOM
> reaper failed to reclaim memory and set MMF_OOM_SKIP.
> This can be confusing/or perhaps even misleading, to the reader of the
> OOM report. Now, we already unconditionally display a task's
> oom_score_adj_min value that can be set to OOM_SCORE_ADJ_MIN which is
> indicative of an "unkillable" task i.e. is not eligible.
>
> This patch provides a clear indication with regard to the OOM
> eligibility of each displayed task.
>
> Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
> ---
>   mm/oom_kill.c | 31 +++++++++++++++++++++++++++----
>   1 file changed, 27 insertions(+), 4 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index eefd3f5fde46..70781d681a6e 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -160,6 +160,27 @@ static inline bool is_sysrq_oom(struct oom_control *oc)
>   	return oc->order == -1;
>   }
>   
> +/**
> + * is_task_eligible_oom - determine if and why a task cannot be OOM killed
> + * @tsk: task to check
> + *
> + * Needs to be called with task_lock().
> + */
> +static const char * is_task_oom_eligible(struct task_struct *p)
> +{
> +	long adj;
> +
> +	adj = (long)p->signal->oom_score_adj;
> +	if (adj == OOM_SCORE_ADJ_MIN)
> +		return "no: oom score";
> +	else if (test_bit(MMF_OOM_SKIP, &p->mm->flags)
> +		return "no: oom reaped";
> +	else if (in_vfork(p))
> +		return "no: in vfork";
> +	else
> +		return "yes";
> +}
> +
>   /* return true if the task is not adequate as candidate victim task. */
>   static bool oom_unkillable_task(struct task_struct *p)
>   {
> @@ -401,12 +422,13 @@ static int dump_task(struct task_struct *p, void *arg)
>   		return 0;
>   	}
>   
> -	pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu         %5hd %s\n",
> +	pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu         %5hd %-15s %s\n",
>   		task->pid, from_kuid(&init_user_ns, task_uid(task)),
>   		task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
>   		mm_pgtables_bytes(task->mm),
>   		get_mm_counter(task->mm, MM_SWAPENTS),
> -		task->signal->oom_score_adj, task->comm);
> +		task->signal->oom_score_adj, is_task_oom_eligible(task),
> +		task->comm);
>   	task_unlock(task);
>   
>   	return 0;
> @@ -420,12 +442,13 @@ static int dump_task(struct task_struct *p, void *arg)
>    * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
>    * are not shown.
>    * State information includes task's pid, uid, tgid, vm size, rss,
> - * pgtables_bytes, swapents, oom_score_adj value, and name.
> + * pgtables_bytes, swapents, oom_score_adj value, oom eligible status
> + * and name.
>    */
>   static void dump_tasks(struct oom_control *oc)
>   {
>   	pr_info("Tasks state (memory values in pages):\n");
> -	pr_info("[  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name\n");
> +	pr_info("[  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj oom eligible? name\n");

A minor nit:

"oom eligible?" has 13 characters. The field width is 15. Maybe you 
should pad 2 more spaces to make the proper alignment.

Cheers,
Longman