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Date: Fri, 20 Jan 2017 02:02:47 -0800 (PST)
From: David Rientjes <rientjes@google.com>
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To: Vlastimil Babka <vbabka@suse.cz>
cc: Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>,
        Mel Gorman <mgorman@suse.de>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>
Subject: Re: [patch] mm, oom: header nodemask is NULL when cpusets are
 disabled
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On Fri, 20 Jan 2017, Vlastimil Babka wrote:

> Could we simplify both patches with something like this?
> Although the sizeof("null") is not the nicest thing, because it relies on knowledge
> that pointer() in lib/vsprintf.c uses this string. Maybe Rasmus has some better idea?
> 
> Thanks,
> Vlastimil
> 
> diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
> index f746e44d4046..4add88ef63f0 100644
> --- a/include/linux/nodemask.h
> +++ b/include/linux/nodemask.h
> @@ -103,7 +103,7 @@ extern nodemask_t _unused_nodemask_arg_;
>   *
>   * Can be used to provide arguments for '%*pb[l]' when printing a nodemask.
>   */
> -#define nodemask_pr_args(maskp)		MAX_NUMNODES, (maskp)->bits
> +#define nodemask_pr_args(maskp)		((maskp) ? MAX_NUMNODES : (int) sizeof("null")), ((maskp) ? (maskp)->bits : NULL)
>  
>  /*
>   * The inline keyword gives the compiler room to decide to inline, or
> 

That's creative.  I'm not sure if it's worth it considering 
nodemask_pr_args() is usually used in a context where we know we have a 
nodemask :)  These would be the only two exceptions.