linux-kernel - Re: [PATCH v1] drivers/base/node.c: get rid of get_nid_for

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Date:   Thu, 28 Nov 2019 11:20:51 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1] drivers/base/node.c: get rid of get_nid_for_pfn()

On Wed 27-11-19 18:41:26, David Hildenbrand wrote:
> Since commit d84f2f5a7552 ("drivers/base/node.c: simplify
> unregister_memory_block_under_nodes()") we only have a single user of
> get_nid_for_pfn(). Let's just inline that code and get rid of
> get_nid_for_pfn().
> 
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: David Hildenbrand <david@...hat.com>

I am not really sure this is an improvement. The code is ugly as hell
and open coding it just makes register_mem_sect_under_node harder to
read.

If anything get_nid_for_pfn deserves a comment why
CONFIG_DEFERRED_STRUCT_PAGE_INIT calls for special case as
early_pfn_to_nid is not bound to that config (it is defined when
CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID || CONFIG_HAVE_MEMBLOCK_NODE_MAP

> ---
>  drivers/base/node.c | 23 +++++++----------------
>  1 file changed, 7 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 98a31bafc8a2..735073fd2926 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -744,17 +744,6 @@ int unregister_cpu_under_node(unsigned int cpu, unsigned int nid)
>  }
>  
>  #ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
> -static int __ref get_nid_for_pfn(unsigned long pfn)
> -{
> -	if (!pfn_valid_within(pfn))
> -		return -1;
> -#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> -	if (system_state < SYSTEM_RUNNING)
> -		return early_pfn_to_nid(pfn);
> -#endif
> -	return pfn_to_nid(pfn);
> -}
> -
>  /* register memory section under specified node if it spans that node */
>  static int register_mem_sect_under_node(struct memory_block *mem_blk,
>  					 void *arg)
> @@ -766,8 +755,6 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
>  	unsigned long pfn;
>  
>  	for (pfn = start_pfn; pfn <= end_pfn; pfn++) {
> -		int page_nid;
> -
>  		/*
>  		 * memory block could have several absent sections from start.
>  		 * skip pfn range from absent section
> @@ -784,11 +771,15 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
>  		 * block belong to the same node.
>  		 */
>  		if (system_state == SYSTEM_BOOTING) {
> -			page_nid = get_nid_for_pfn(pfn);
> -			if (page_nid < 0)
> +			if (!pfn_valid_within(pfn))
>  				continue;
> -			if (page_nid != nid)
> +#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> +			if (early_pfn_to_nid(pfn) != nid)
>  				continue;
> +#else
> +			if (pfn_to_nid(pfn) != nid)
> +				continue;
> +#endif
>  		}
>  
>  		/*
> -- 
> 2.21.0

-- 
Michal Hocko
SUSE Labs