linux-kernel - Re: [RFT PATCH v2 4/5] mm: provide more accurate estimation of pages occupied by memmap

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Date:	Thu, 29 Nov 2012 10:25:01 +0800
From:	Jianguo Wu <wujianguo@...wei.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Jiang Liu <liuj97@...il.com>, Wen Congyang <wency@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Chris Clayton <chris2553@...glemail.com>,
	"Rafael J . Wysocki" <rjw@...k.pl>, Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan@...nel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFT PATCH v2 4/5] mm: provide more accurate estimation of pages
 occupied by memmap

On 2012/11/29 7:52, Andrew Morton wrote:

> On Wed, 21 Nov 2012 23:09:46 +0800
> Jiang Liu <liuj97@...il.com> wrote:
> 
>> Subject: Re: [RFT PATCH v2 4/5] mm: provide more accurate estimation of pages occupied by memmap
> 
> How are people to test this?  "does it boot"?
> 

I have tested this in x86_64, it does boot.

Node 0, zone      DMA
  pages free     3972
        min      1
        low      1
        high     1
        scanned  0
        spanned  4080
        present  3979
        managed  3972

Node 0, zone    DMA32
  pages free     448783
        min      172
        low      215
        high     258
        scanned  0
        spanned  1044480
        present  500799
        managed  444545

Node 0, zone   Normal
  pages free     2375547
        min      1394
        low      1742
        high     2091
        scanned  0
        spanned  3670016
        present  3670016
        managed  3585105

Thanks,
Jianguo Wu

>> If SPARSEMEM is enabled, it won't build page structures for
>> non-existing pages (holes) within a zone, so provide a more accurate
>> estimation of pages occupied by memmap if there are bigger holes within
>> the zone.
>>
>> And pages for highmem zones' memmap will be allocated from lowmem, so
>> charge nr_kernel_pages for that.
>>
>> ...
>>
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -4442,6 +4442,26 @@ void __init set_pageblock_order(void)
>>  
>>  #endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
>>  
>> +static unsigned long calc_memmap_size(unsigned long spanned_pages,
>> +				      unsigned long present_pages)
>> +{
>> +	unsigned long pages = spanned_pages;
>> +
>> +	/*
>> +	 * Provide a more accurate estimation if there are holes within
>> +	 * the zone and SPARSEMEM is in use. If there are holes within the
>> +	 * zone, each populated memory region may cost us one or two extra
>> +	 * memmap pages due to alignment because memmap pages for each
>> +	 * populated regions may not naturally algined on page boundary.
>> +	 * So the (present_pages >> 4) heuristic is a tradeoff for that.
>> +	 */
>> +	if (spanned_pages > present_pages + (present_pages >> 4) &&
>> +	    IS_ENABLED(CONFIG_SPARSEMEM))
>> +		pages = present_pages;
>> +
>> +	return PAGE_ALIGN(pages * sizeof(struct page)) >> PAGE_SHIFT;
>> +}
>> +
> 
> I spose we should do this, although it makes no difference as the
> compiler will inline calc_memmap_size() into its caller:
> 
> --- a/mm/page_alloc.c~mm-provide-more-accurate-estimation-of-pages-occupied-by-memmap-fix
> +++ a/mm/page_alloc.c
> @@ -4526,8 +4526,8 @@ void __init set_pageblock_order(void)
>  
>  #endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */
>  
> -static unsigned long calc_memmap_size(unsigned long spanned_pages,
> -				      unsigned long present_pages)
> +static unsigned long __paginginit calc_memmap_size(unsigned long spanned_pages,
> +						   unsigned long present_pages)
>  {
>  	unsigned long pages = spanned_pages;
>  
> 
> 
> .
> 



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