linux-kernel - Re: [PATCH] mm/sparse: clarify pgdat_to

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Date:   Fri, 2 Jul 2021 16:11:06 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Miles Chen <miles.chen@...iatek.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        wsd_upstream@...iatek.com
Subject: Re: [PATCH] mm/sparse: clarify pgdat_to_phys

On Wed, Jun 30, 2021 at 05:23:09PM +0800, Miles Chen wrote:
> clarify pgdat_to_phys() by wrapping pgdat_to_phys
> with CONFIG_NUMA. (the same config as contig_page_data)
> 
> No functional change intended.
> 
> Comment from Mark [1]:
> "
> ... and I reckon it'd be clearer and more robust to define
> pgdat_to_phys() in the same ifdefs as contig_page_data so
> that these, stay in-sync. e.g. have:
> 
> | #ifdef CONFIG_NUMA
> | #define pgdat_to_phys(x)	virt_to_phys(x)
> | #else /* CONFIG_NUMA */
> |
> | extern struct pglist_data contig_page_data;
> | ...
> | #define pgdat_to_phys(x)	__pa_symbol(&contig_page_data)
> |
> | #endif /* CONIFIG_NUMA */
> "
> 
> [1] https://lore.kernel.org/linux-arm-kernel/20210615131902.GB47121@C02TD0UTHF1T.local/
> 
> Cc: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Miles Chen <miles.chen@...iatek.com>
> ---
>  mm/sparse.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 7272f7a1449d..62c21ec28e33 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -344,14 +344,15 @@ size_t mem_section_usage_size(void)
>  	return sizeof(struct mem_section_usage) + usemap_size();
>  }
>  
> -static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
> -{
> -#ifndef CONFIG_NUMA
> -	return __pa_symbol(pgdat);
> -#else
> -	return __pa(pgdat);
> -#endif
> -}
> +#ifdef CONFIG_NUMA
> +#define pgdat_to_phys(pgdat) __pa(pgdat)
> +#else /* CONFIG_NUMA */
> +/*
> + * When !CONFIG_NUMA, we only expect pgdat == &contig_page_data,
> + * and use __pa_symbol().
> + */
> +#define pgdat_to_phys(pgdat) __pa_symbol(pgdat)
> +#endif /* CONFIG_NUMA */

I'm not sure a macro is better than a static inline.

Maybe we'd want to warn if pgdat passed to pgtat_to_phys() is not
&contig_page_data, e.g something like

static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
{
	if (!IS_ENABLED(CONFIG_NUMA)) {
		if (pgdat == &contig_page_data)
			return __pa_symbol(&contig_page_data);
		else
			pr_warn("Unexpected pglist_data pointer!\n");
	}
	
	return __pa(pgdat);
}
  
>  #ifdef CONFIG_MEMORY_HOTREMOVE
>  static struct mem_section_usage * __init
> -- 
> 2.18.0
> 

-- 
Sincerely yours,
Mike.