Re: [PATCH 3/3] mm, meminit: Allow early_pfn_to_nid to be used during runtime

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 3/3] mm, meminit: Allow early_pfn_to_nid to be used during runtime
Date	2015-07-17 15:20 +0200
Message-ID	<pNdIv-6vu-29@gated-at.bofh.it> (permalink)
References	<pNcW6-5lc-7@gated-at.bofh.it> <pNcW6-5lc-13@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, Jul 17, 2015 at 01:22:04PM +0100, Mel Gorman wrote:
>  int __meminit early_pfn_to_nid(unsigned long pfn)
>  {
> +	static DEFINE_SPINLOCK(early_pfn_lock);
>  	int nid;
>  
> -	/* The system will behave unpredictably otherwise */
> -	BUG_ON(system_state != SYSTEM_BOOTING);
> +	/* Avoid locking overhead during boot but hotplug must lock */
> +	if (system_state != SYSTEM_BOOTING)
> +		spin_lock(&early_pfn_lock);
>  
>  	nid = __early_pfn_to_nid(pfn, &early_pfnnid_cache);
> -	if (nid >= 0)
> -		return nid;
> -	/* just returns 0 */
> -	return 0;
> +	if (nid < 0)
> +		nid = 0;
> +
> +	if (system_state != SYSTEM_BOOTING)
> +		spin_unlock(&early_pfn_lock);
> +
> +	return nid;
>  }

Why the conditional locking?
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[PATCH 3/3] mm, meminit: Allow early_pfn_to_nid to be used during runtime Mel Gorman <mgorman@suse.de> - 2015-07-17 14:30 +0200
  Re: [PATCH 3/3] mm, meminit: Allow early_pfn_to_nid to be used  during runtime Mel Gorman <mgorman@suse.de> - 2015-07-17 15:20 +0200
    Re: [PATCH 3/3] mm, meminit: Allow early_pfn_to_nid to be used  during runtime Peter Zijlstra <peterz@infradead.org> - 2015-07-17 15:30 +0200
      Re: [PATCH 3/3] mm, meminit: Allow early_pfn_to_nid to be used  during runtime Mel Gorman <mgorman@suse.de> - 2015-07-17 15:40 +0200
        Re: [PATCH 3/3] mm, meminit: Allow early_pfn_to_nid to be used  during runtime Peter Zijlstra <peterz@infradead.org> - 2015-07-17 16:00 +0200
  Re: [PATCH 3/3] mm, meminit: Allow early_pfn_to_nid to be used  during runtime Peter Zijlstra <peterz@infradead.org> - 2015-07-17 15:20 +0200

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