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Date:   Thu, 09 Nov 2017 08:27:33 -0800
From:   Joe Perches <joe@...ches.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/page_alloc: Avoid KERN_CONT uses in warn_alloc

On Thu, 2017-11-09 at 11:05 +0100, Michal Hocko wrote:
[]
> Subject: [PATCH] mm: simplify nodemask printing
> 
> alloc_warn and dump_header have to explicitly handle NULL nodemask which
> forces both paths to use pr_cont. We can do better. printk already
> handles NULL pointers properly so all what we need is to teach
> nodemask_pr_args to handle NULL nodemask carefully. This allows
> simplification of both alloc_warn and dump_header and get rid of pr_cont
> altogether.
[]
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
[]
> @@ -426,14 +426,10 @@ static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
>  
>  static void dump_header(struct oom_control *oc, struct task_struct *p)
>  {
> -	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)");
> -	pr_cont(",  order=%d, oom_score_adj=%hd\n",
> -		oc->order, current->signal->oom_score_adj);
> +	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(oc->nodemask), oc->order,
> +			current->signal->oom_score_adj);

trivia:

You could align the arguments to the open parenthesis here

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
[]
> @@ -3281,20 +3281,14 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
>  	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs))
>  		return;
>  
> -	pr_warn("%s: ", current->comm);
> -
>  	va_start(args, fmt);
>  	vaf.fmt = fmt;
>  	vaf.va = &args;
> -	pr_cont("%pV", &vaf);
> +	pr_warn("%s: %pV, mode:%#x(%pGg), nodemask=%*pbl\n",
> +			current->comm, &vaf, gfp_mask, &gfp_mask,
> +			nodemask_pr_args(nodemask));

and here

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