Re: [PATCH] mm, page_alloc: cleanup usemap_size() when SPARSEMEM is not set

[Wei Yang <richard.weiyang@gmail.com>]

On Tue, Jan 22, 2019 at 09:55:24AM +0100, Michal Hocko wrote:
>On Sat 19-01-19 07:49:05, Wei Yang wrote:
>> Two cleanups in this patch:
>> 
>>   * since pageblock_nr_pages == (1 << pageblock_order), the roundup()
>>     and right shift pageblock_order could be replaced with
>>     DIV_ROUND_UP()
>
>Why is this change worth it?
>

To make it directly show usemapsize is number of times of
pageblock_nr_pages.

>>   * use BITS_TO_LONGS() to get number of bytes for bitmap
>> 
>> This patch also fix one typo in comment.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> ---
>>  mm/page_alloc.c | 9 +++------
>>  1 file changed, 3 insertions(+), 6 deletions(-)
>> 
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index d295c9bc01a8..d7073cedd087 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6352,7 +6352,7 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
>>  /*
>>   * Calculate the size of the zone->blockflags rounded to an unsigned long
>>   * Start by making sure zonesize is a multiple of pageblock_order by rounding
>> - * up. Then use 1 NR_PAGEBLOCK_BITS worth of bits per pageblock, finally
>> + * up. Then use 1 NR_PAGEBLOCK_BITS width of bits per pageblock, finally
>
>why do you change this?
>

Is the original comment not correct? Or I misunderstand the English
word?

>>   * round what is now in bits to nearest long in bits, then return it in
>>   * bytes.
>>   */
>> @@ -6361,12 +6361,9 @@ static unsigned long __init usemap_size(unsigned long zone_start_pfn, unsigned l
>>  	unsigned long usemapsize;
>>  
>>  	zonesize += zone_start_pfn & (pageblock_nr_pages-1);
>> -	usemapsize = roundup(zonesize, pageblock_nr_pages);
>> -	usemapsize = usemapsize >> pageblock_order;
>> +	usemapsize = DIV_ROUND_UP(zonesize, pageblock_nr_pages);
>>  	usemapsize *= NR_PAGEBLOCK_BITS;
>> -	usemapsize = roundup(usemapsize, 8 * sizeof(unsigned long));
>> -
>> -	return usemapsize / 8;
>> +	return BITS_TO_LONGS(usemapsize) * sizeof(unsigned long);
>>  }
>>  
>>  static void __ref setup_usemap(struct pglist_data *pgdat,
>> -- 
>> 2.15.1
>> 
>
>-- 
>Michal Hocko
>SUSE Labs

-- 
Wei Yang
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