linux-kernel - Re: [PATCH 2/3] mm/oom_kill: introduce is_sysrq

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Date:	Mon, 21 Sep 2015 18:18:31 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Yaowei Bai <bywxiaobai@....com>
Cc:	akpm@...ux-foundation.org, mgorman@...e.de, rientjes@...gle.com,
	hannes@...xchg.org, vdavydov@...allels.com, oleg@...hat.com,
	vbabka@...e.cz, iamjoonsoo.kim@....com, zhangyanfei@...fujitsu.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm/oom_kill: introduce is_sysrq_oom helper

On Wed 16-09-15 19:59:59, Yaowei Bai wrote:
> Introduce is_sysrq_oom helper function indicating oom kill triggered
> by sysrq to improve readability.
> 
> No functional changes.

I was complaining about a subtle semantic of order -1 when it was
introduced. This is easier to follow. At least for me.
 
> Signed-off-by: Yaowei Bai <bywxiaobai@....com>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/oom_kill.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 1ecc0bc..7b6228e 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -118,6 +118,15 @@ found:
>  	return t;
>  }
>  
> +/*
> + * order == -1 means the oom kill is required by sysrq, otherwise only
> + * for display purposes.
> + */
> +static inline bool is_sysrq_oom(struct oom_control *oc)
> +{
> +	return oc->order == -1;
> +}
> +
>  /* return true if the task is not adequate as candidate victim task. */
>  static bool oom_unkillable_task(struct task_struct *p,
>  		struct mem_cgroup *memcg, const nodemask_t *nodemask)
> @@ -265,7 +274,7 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
>  	 * Don't allow any other task to have access to the reserves.
>  	 */
>  	if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
> -		if (oc->order != -1)
> +		if (!is_sysrq_oom(oc))
>  			return OOM_SCAN_ABORT;
>  	}
>  	if (!task->mm)
> @@ -278,7 +287,7 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
>  	if (oom_task_origin(task))
>  		return OOM_SCAN_SELECT;
>  
> -	if (task_will_free_mem(task) && oc->order != -1)
> +	if (task_will_free_mem(task) && !is_sysrq_oom(oc))
>  		return OOM_SCAN_ABORT;
>  
>  	return OOM_SCAN_OK;
> @@ -608,7 +617,7 @@ void check_panic_on_oom(struct oom_control *oc, enum oom_constraint constraint,
>  			return;
>  	}
>  	/* Do not panic for oom kills triggered by sysrq */
> -	if (oc->order == -1)
> +	if (is_sysrq_oom(oc))
>  		return;
>  	dump_header(oc, NULL, memcg);
>  	panic("Out of memory: %s panic_on_oom is enabled\n",
> @@ -688,7 +697,7 @@ bool out_of_memory(struct oom_control *oc)
>  
>  	p = select_bad_process(oc, &points, totalpages);
>  	/* Found nothing?!?! Either we hang forever, or we panic. */
> -	if (!p && oc->order != -1) {
> +	if (!p && !is_sysrq_oom(oc)) {
>  		dump_header(oc, NULL, NULL);
>  		panic("Out of memory and no killable processes...\n");
>  	}
> -- 
> 1.9.1
> 
> 
> --
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-- 
Michal Hocko
SUSE Labs
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