linux-kernel - Re: [patch] mm, oom: header nodemask is NULL when cpusets are disabled

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Date:   Fri, 20 Jan 2017 15:07:55 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.com>
To:     "'David Rientjes'" <rientjes@...gle.com>,
        "'Andrew Morton'" <akpm@...ux-foundation.org>,
        "'Vlastimil Babka'" <vbabka@...e.cz>
Cc:     "'Michal Hocko'" <mhocko@...nel.org>,
        "'Johannes Weiner'" <hannes@...xchg.org>,
        "'Mel Gorman'" <mgorman@...e.de>, <linux-mm@...ck.org>,
        "'LKML'" <linux-kernel@...r.kernel.org>
Subject: Re: [patch] mm, oom: header nodemask is NULL when cpusets are disabled

On Friday, January 20, 2017 6:58 AM David Rientjes wrote: 
> 
> Commit 82e7d3abec86 ("oom: print nodemask in the oom report") implicitly
> sets the allocation nodemask to cpuset_current_mems_allowed when there is
> no effective mempolicy.  cpuset_current_mems_allowed is only effective
> when cpusets are enabled, which is also printed by dump_header(), so
> setting the nodemask to cpuset_current_mems_allowed is redundant and
> prevents debugging issues where ac->nodemask is not set properly in the
> page allocator.
> 
> This provides better debugging output since
> cpuset_print_current_mems_allowed() is already provided.
> 
> Suggested-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
Acked-by: Hillf Danton <hillf.zj@...baba-inc.com>

>  mm/oom_kill.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -403,12 +403,14 @@ static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
> 
>  static void dump_header(struct oom_control *oc, struct task_struct *p)
>  {
> -	nodemask_t *nm = (oc->nodemask) ? oc->nodemask : &cpuset_current_mems_allowed;
> -
> -	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), nodemask=%*pbl, order=%d, oom_score_adj=%hd\n",
> -		current->comm, oc->gfp_mask, &oc->gfp_mask,
> -		nodemask_pr_args(nm), oc->order,
> -		current->signal->oom_score_adj);
> +	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), nodemask=",
> +		current->comm, oc->gfp_mask, &oc->gfp_mask);
> +	if (oc->nodemask)
> +		pr_cont("%*pbl", nodemask_pr_args(oc->nodemask));
> +	else
> +		pr_cont("(null)\n");

Nit: no newline needed.

> +	pr_cont(",  order=%d, oom_score_adj=%hd\n",
> +		oc->order, current->signal->oom_score_adj);
>  	if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
>  		pr_warn("COMPACTION is disabled!!!\n");
> 
> @@ -417,7 +419,7 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
>  	if (oc->memcg)
>  		mem_cgroup_print_oom_info(oc->memcg, p);
>  	else
> -		show_mem(SHOW_MEM_FILTER_NODES, nm);
> +		show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
>  	if (sysctl_oom_dump_tasks)
>  		dump_tasks(oc->memcg, oc->nodemask);
>  }
>