On Tue, Aug 26, 2008 at 12:53 AM, Ingo Molnar <mingo@elte.hu> wrote:
quoted text
>
> * David Miller <davem@davemloft.net> wrote:
>
>> From: Ingo Molnar <mingo@elte.hu>
>> Date: Tue, 26 Aug 2008 09:22:20 +0200
>>
>> > And i guess the next generation of 4K CPUs support should just get away
>> > from cpumask_t-on-kernel-stack model altogether, as the current model is
>> > not maintainable. We tried the on-kernel-stack variant, and it really
>> > does not work reliably. We can fix this in v2.6.28.
>>
>> I recenetly did some work on sparc64 to use cpumask pointers as much
>> as possible.
>>
>> The only case that didn't work was due to a limitation in arch
>> interfaces for the new generic smp_call_function() code. It passes a
>> cpumask_t instead of a pointer to one via
>> arch_send_call_function_ipi().
>>
>> But other than that, the whole sparc64 SMP stuff uses cpumask_t
>> pointers only.

wonder if could use "unsigned long *" directly.
so could dyn_array directly like

int cpumask_size;

unsigned long *online_cpu_map;
DEFINE_DYN_ARRAY(online_cpu_map, sizeof(unsigned long), cpumask_size,
PAGE_SIZE, NULL);

and after nr_cpu_ids is assigned, have
cpumask_size = (nr_cpu_ids + sizeof(unsigned long) - 1)/sizeof(unsigned long);

then we could NR_CPUS=4096 kernel to small system. ...

YH
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