Re: [PATCH 2/5] mm/sparse: optimize sparse_index_alloc

[Gavin Shan <shangw@linux.vnet.ibm.com>]

>> With CONFIG_SPARSEMEM_EXTREME, the two level of memory section
>> descriptors are allocated from slab or bootmem. When allocating
>> from slab, let slab allocator to clear the memory chunk. However,
>> the memory chunk from bootmem allocator, we have to clear that
>> explicitly.
>
>I am sorry but I do not see how this optimize the current code. What is
>the difference between slab doing memset and doing it explicitly for all
>cases?
>

Yeah, I do agree it won't do much optimization here. However, I'm wandering
if I can remove the whole peice of code doing memset(setion, 0, array_size)
since it seems that alloc_bootmem_node() also clears the allocated memory
chunk :-)

Please correct me if I'm wrong about alloc_bootmem_node() :-)

Thanks,
Gavin

>> 
>> Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
>> ---
>>  mm/sparse.c |   12 ++++++------
>>  1 file changed, 6 insertions(+), 6 deletions(-)
>> 
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index afd0998..ce50c8b 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -74,14 +74,14 @@ static struct mem_section noinline __init_refok *sparse_index_alloc(int nid)
>>  
>>  	if (slab_is_available()) {
>>  		if (node_state(nid, N_HIGH_MEMORY))
>> -			section = kmalloc_node(array_size, GFP_KERNEL, nid);
>> +			section = kzalloc_node(array_size, GFP_KERNEL, nid);
>>  		else
>> -			section = kmalloc(array_size, GFP_KERNEL);
>> -	} else
>> +			section = kzalloc(array_size, GFP_KERNEL);
>> +	} else {
>>  		section = alloc_bootmem_node(NODE_DATA(nid), array_size);
>> -
>> -	if (section)
>> -		memset(section, 0, array_size);
>> +		if (section)
>> +			memset(section, 0, array_size);
>> +	}
>>  
>>  	return section;
>>  }
>> -- 
>> 1.7.9.5
>> 
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>
>-- 
>Michal Hocko
>SUSE Labs
>SUSE LINUX s.r.o.
>Lihovarska 1060/12
>190 00 Praha 9    
>Czech Republic
>
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