linux-kernel - Re: [PATCH] ARM: mm: Regarding section when dealing with meminfo

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Date:	Thu, 20 Jan 2011 23:28:44 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KyongHo Cho <pullip.cho@...sung.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	Kukjin Kim <kgene.kim@...sung.com>,
	Ilho Lee <ilho215.lee@...sung.com>,
	KeyYoung Park <keyyoung.park@...sung.com>
Subject: Re: [PATCH] ARM: mm: Regarding section when dealing with meminfo

On Thu, Jan 20, 2011 at 06:45:39PM +0900, KyongHo Cho wrote:
> Sparsemem allows that a bank of memory spans over several adjacent
> sections if the start address and the end address of the bank
> belong to different sections.
> When gathering statictics of physical memory in mem_init() and
> show_mem(), this possiblity was not considered.

Please write down the result if we doesn't consider this patch.
I can understand what happens but for making good description and review,
merging easily, it would be better to write down the result without 
the patch explicitly.

> 
> This patch guarantees that simple increasing the pointer to page
> descriptors does not exceed the boundary of a section.
> 
> Signed-off-by: KyongHo Cho <pullip.cho@...sung.com>
> ---
>  arch/arm/mm/init.c |   74 +++++++++++++++++++++++++++++++++++----------------
>  1 files changed, 51 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index 57c4c5c..6ccecbe 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -93,24 +93,38 @@ void show_mem(void)
>  
>  		pfn1 = bank_pfn_start(bank);
>  		pfn2 = bank_pfn_end(bank);
> -
> +#ifndef CONFIG_SPARSEMEM
>  		page = pfn_to_page(pfn1);
>  		end  = pfn_to_page(pfn2 - 1) + 1;
> -
> +#else
> +		pfn2--;
>  		do {
> -			total++;
> -			if (PageReserved(page))
> -				reserved++;
> -			else if (PageSwapCache(page))
> -				cached++;
> -			else if (PageSlab(page))
> -				slab++;
> -			else if (!page_count(page))
> -				free++;
> -			else
> -				shared += page_count(page) - 1;
> -			page++;
> -		} while (page < end);
> +			page = pfn_to_page(pfn1);
> +			if (pfn_to_section_nr(pfn1) < pfn_to_section_nr(pfn2)) {
> +				pfn1 += PAGES_PER_SECTION;
> +				pfn1 &= PAGE_SECTION_MASK;
> +			} else {
> +				pfn1 = pfn2;
> +			}
> +			end = pfn_to_page(pfn1) + 1;
> +#endif
> +			do {
> +				total++;
> +				if (PageReserved(page))
> +					reserved++;
> +				else if (PageSwapCache(page))
> +					cached++;
> +				else if (PageSlab(page))
> +					slab++;
> +				else if (!page_count(page))
> +					free++;
> +				else
> +					shared += page_count(page) - 1;
> +				page++;
> +			} while (page < end);
> +#ifdef CONFIG_SPARSEMEM
> +		} while (pfn1 < pfn2);
> +#endif
>  	}
>  
>  	printk("%d pages of RAM\n", total);
> @@ -470,17 +484,31 @@ void __init mem_init(void)
>  
>  		pfn1 = bank_pfn_start(bank);
>  		pfn2 = bank_pfn_end(bank);
> -
> +#ifndef CONFIG_SPARSEMEM
>  		page = pfn_to_page(pfn1);
>  		end  = pfn_to_page(pfn2 - 1) + 1;
> -
> +#else
> +		pfn2--;
>  		do {
> -			if (PageReserved(page))
> -				reserved_pages++;
> -			else if (!page_count(page))
> -				free_pages++;
> -			page++;
> -		} while (page < end);
> +			page = pfn_to_page(pfn1);
> +			if (pfn_to_section_nr(pfn1) < pfn_to_section_nr(pfn2)) {
> +				pfn1 += PAGES_PER_SECTION;
> +				pfn1 &= PAGE_SECTION_MASK;
> +			} else {
> +				pfn1 = pfn2;
> +			}
> +			end = pfn_to_page(pfn1) + 1;
> +#endif
> +			do {
> +				if (PageReserved(page))
> +					reserved_pages++;
> +				else if (!page_count(page))
> +					free_pages++;
> +				page++;
> +			} while (page < end);
> +#ifdef CONFIG_SPARSEMEM
> +		} while (pfn1 < pfn2);
> +#endif
>  	}

Hmm.. new ifndef magic makes code readability bad.
Couldn't we do it by simple pfn iterator not page and pfn_valid check?

>  
>  	/*
> -- 
> 1.6.2.5
> 
> --
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-- 
Kind regards,
Minchan Kim
--
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