Re: [PATCH] percpu data: only iterate over possible CPUs

[Eric Dumazet <dada1@cosmosbay.com>]

Heiko Carstens a écrit :
>> for (cpu = max_cpus ; cpu < NR_CPUS ; cpu++)
>> 	cpu_clear(cpu, cpu_possible_map);
> 
> Hmm... I don't think the semantics of cpu_possible_map allow to change it.
> Also any code that uses for_each_cpu() may allocate memory _before_
> cpu_possible_map is changed back to reflect a smaller number of cpus.
> Doesn't look like the correct way to fix this.
> Thinking a bit longer this was probably a reason why initialization of
> this map was done in smp_prepare_cpus() before it silently moved to
> setup_arch().

Hum... of course you may loose some bits of memory (percpu data for example) 
but clearing a cpu in cpu_possible_map is allowed.

See arch/alpha/kernel/process.c and arch/x86_64/kernel/smpboot.c for uses of 
cpu_clear()