Re: [S+Q 02/16] [PATCH 1/2] percpu: make @dyn_size always mean min dyn_size in first chunk init functions

[Tejun Heo <tj@kernel.org>]

Hello,

On 06/27/2010 07:06 AM, David Rientjes wrote:
> On Fri, 25 Jun 2010, Christoph Lameter wrote:
> 
>> In pcpu_alloc_info()
> 
> You mean pcpu_build_alloc_info()?

Yeap.

>> @@ -105,7 +105,7 @@ extern struct pcpu_alloc_info * __init p
>>  extern void __init pcpu_free_alloc_info(struct pcpu_alloc_info *ai);
>>  
>>  extern struct pcpu_alloc_info * __init pcpu_build_alloc_info(
>> -				size_t reserved_size, ssize_t dyn_size,
>> +				size_t reserved_size, size_t dyn_size,
>>  				size_t atom_size,
>>  				pcpu_fc_cpu_distance_fn_t cpu_distance_fn);
>>  
> 
> This can just be removed entirely, it's unnecessarily global.

Oh yeah, it's not used outside mm/percpu.c anymore.  I'll make it
static.

>>  /**
>>   * pcpu_alloc_alloc_info - allocate percpu allocation info
>>   * @nr_groups: the number of groups
>> @@ -1060,7 +1046,7 @@ void __init pcpu_free_alloc_info(struct 
>>  /**
>>   * pcpu_build_alloc_info - build alloc_info considering distances between CPUs
>>   * @reserved_size: the size of reserved percpu area in bytes
>> - * @dyn_size: free size for dynamic allocation in bytes, -1 for auto
>> + * @dyn_size: free size for dynamic allocation in bytes
> 
> It's the minimum free size, it's not necessarily the exact size due to 
> round-up.

Will update.

>>  struct pcpu_alloc_info * __init pcpu_build_alloc_info(
>> -				size_t reserved_size, ssize_t dyn_size,
>> +				size_t reserved_size, size_t dyn_size,
>>  				size_t atom_size,
>>  				pcpu_fc_cpu_distance_fn_t cpu_distance_fn)
>>  {
>> @@ -1098,13 +1084,15 @@ struct pcpu_alloc_info * __init pcpu_bui
>>  	memset(group_map, 0, sizeof(group_map));
>>  	memset(group_cnt, 0, sizeof(group_map));
>>  
>> +	size_sum = PFN_ALIGN(static_size + reserved_size + dyn_size);
>> +	dyn_size = size_sum - static_size - reserved_size;
> 
> Ok, so the only purpose of "dyn_size" is to store in the struct 
> pcpu_alloc_info later.  Before this patch, ai->dyn_size would always be 0 
> if that's what was passed to pcpu_build_alloc_info(), but due to this 
> arithmetic it now requires that static_size + reserved_size to be pfn 
> aligned.  Where is that enforced or do we not care?

I'm not really following you, but

* Nobody called pcpu_build_alloc_info() w/ zero dyn_size.  It was
  either -1 or positive minimum size.

* None of static_size, reserved_size or dyn_size needs to be page
  aligned.

Thanks for the review.

-- 
tejun

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