Re: [PATCH 34/35] x86: use num_processors for possible cpus

[H. Peter Anvin]

On 02/18/2010 11:48 AM, Christoph Lameter wrote:
>>
>> Yes, and I have repeatedly requested that we allocate the memory on the
>> first up of a disabled CPU rather than eagerly, but in *most*
>> configurations the amount is relatively small.
> 
> The size of the static per cpu segment is likely around 30k and you will
> likely add another 30k in dynamic allocations.
> 
> As I have also repeatedly stated: Dynamic percpu data allocation when
> onlining / offlining processors will complicate locking (cannot rely on
> percpu be present anymore) and introduce numerous additional
> hotplug notifiers into subsystems.

I did state explicitly "on first up".  Trying to free it would be
insane.  There are a couple of subsystems which are percpu memory
pigs... so far it's not clear any of them actually matters in a
production kernel.  60K * 16 phantom processors is still ~ 1 MB, which
probably isn't enough to worry about but isn't great.

	-hpa
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