linux-kernel - Re: [PATCH v4, part3 13/41] mm/ARM: prepare for removing num_physpages and simplify mem

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Date:	Sat, 20 Apr 2013 23:19:58 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	David Rientjes <rientjes@...gle.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	David Howells <dhowells@...hat.com>,
	Mark Salter <msalter@...hat.com>,
	Jianguo Wu <wujianguo@...wei.com>, linux-mm@...ck.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4, part3 13/41] mm/ARM: prepare for removing num_physpages
 and simplify mem_init()

On 04/20/2013 12:54 AM, Russell King - ARM Linux wrote:
> On Sat, Apr 06, 2013 at 10:32:12PM +0800, Jiang Liu wrote:
>> Prepare for removing num_physpages and simplify mem_init().
>>
>> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
>> Cc: Russell King <linux@....linux.org.uk>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will.deacon@....com>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: linux-kernel@...r.kernel.org
>> ---
>>  arch/arm/mm/init.c |   47 ++---------------------------------------------
>>  1 file changed, 2 insertions(+), 45 deletions(-)
>>
>> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
>> index add4fcb..7a911d1 100644
>> --- a/arch/arm/mm/init.c
>> +++ b/arch/arm/mm/init.c
>> @@ -582,9 +582,6 @@ static void __init free_highpages(void)
>>   */
>>  void __init mem_init(void)
>>  {
>> -	unsigned long reserved_pages, free_pages;
>> -	struct memblock_region *reg;
>> -	int i;
>>  #ifdef CONFIG_HAVE_TCM
>>  	/* These pointers are filled in on TCM detection */
>>  	extern u32 dtcm_end;
>> @@ -605,47 +602,7 @@ void __init mem_init(void)
>>  
>>  	free_highpages();
>>  
>> -	reserved_pages = free_pages = 0;
>> -
>> -	for_each_bank(i, &meminfo) {
>> -		struct membank *bank = &meminfo.bank[i];
>> -		unsigned int pfn1, pfn2;
>> -		struct page *page, *end;
>> -
>> -		pfn1 = bank_pfn_start(bank);
>> -		pfn2 = bank_pfn_end(bank);
>> -
>> -		page = pfn_to_page(pfn1);
>> -		end  = pfn_to_page(pfn2 - 1) + 1;
>> -
>> -		do {
>> -			if (PageReserved(page))
>> -				reserved_pages++;
>> -			else if (!page_count(page))
>> -				free_pages++;
>> -			page++;
>> -		} while (page < end);
>> -	}
>> -
>> -	/*
>> -	 * Since our memory may not be contiguous, calculate the
>> -	 * real number of pages we have in this system
>> -	 */
>> -	printk(KERN_INFO "Memory:");
>> -	num_physpages = 0;
>> -	for_each_memblock(memory, reg) {
>> -		unsigned long pages = memblock_region_memory_end_pfn(reg) -
>> -			memblock_region_memory_base_pfn(reg);
>> -		num_physpages += pages;
>> -		printk(" %ldMB", pages >> (20 - PAGE_SHIFT));
>> -	}
>> -	printk(" = %luMB total\n", num_physpages >> (20 - PAGE_SHIFT));
>> -
>> -	printk(KERN_NOTICE "Memory: %luk/%luk available, %luk reserved, %luK highmem\n",
>> -		nr_free_pages() << (PAGE_SHIFT-10),
>> -		free_pages << (PAGE_SHIFT-10),
>> -		reserved_pages << (PAGE_SHIFT-10),
>> -		totalhigh_pages << (PAGE_SHIFT-10));
>> +	mem_init_print_info(NULL);
> 
> I'm concerned about this.  We explicitly do not use the memblock information
> when walking the memory above for the reserved/free pages because memblock
> merges the various banks of memory together - and those may cross sparsemem
> boundaries.  Any crossing of the sparsemem boundaries needs the struct page
> pointer to be re-evaluated because it can be part of a different array of
> such things.
> 
> Where's the rest of the patches?
> 
Hi Russel,
	Thanks for review the patch. You may find the patch introducing 
mem_init_print_info() at: http://marc.info/?l=linux-mm&m=136525938817934&w=2
Basically it prints standard memory statistics info as below for all architectures
without walking the page structure array.
Memory: 7744624K/8074824K available (6969K kernel code, 1011K data, 2828K rodata, 1016K init, 9640K bss, 330200K reserved)

On the other hand, the patch does change information printed on boot, especially
it doesn't print size of each memory block. If needed, I can revert the code to
print size of each memory block.

	Regards!
	Gerry



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