Re: [patch 02/41] cpu alloc: The allocator

Mike Travis
2008-06-04T14:58:26Z

Christoph Lameter wrote:
> On Fri, 30 May 2008, Eric Dumazet wrote:
>
>>> +static DEFINE_PER_CPU(UNIT_TYPE, area[UNITS]);
>>>
>> area[] is not guaranteed to be aligned on anything but 4 bytes.
>>
>> If someone then needs to call cpu_alloc(8, GFP_KERNEL, 8), it might get an non
>> aligned result.
>>
>> Either you should add an __attribute__((__aligned__(PAGE_SIZE))),
>> or take into account the real address of area[] in cpu_alloc() to avoid waste
>> of up to PAGE_SIZE bytes
>> per cpu.
>
> I think cacheline aligning should be sufficient. People should not
> allocate large page aligned objects here.

I'm a bit confused. Why is DEFINE_PER_CPU_SHARED_ALIGNED() conditioned on
ifdef MODULE?

#ifdef MODULE
#define SHARED_ALIGNED_SECTION ".data.percpu"
#else
#define SHARED_ALIGNED_SECTION ".data.percpu.shared_aligned"
#endif

#define DEFINE_PER_CPU_SHARED_ALIGNED(type, name) \
__attribute__((__section__(SHARED_ALIGNED_SECTION))) \
PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name \
____cacheline_aligned_in_smp

Thanks,
Mike