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

Eric Dumazet
2008-05-30T05:55:07Z

Christoph Lameter a écrit :
> 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.
>
>
>
Hum, maybe, but then we broke modules that might request up to PAGE_SIZE
alignement for their percpu section,
if I read your 3rd patch correctly.

Taking into account the ((unsigned long)area & (PAGE_SIZE-1)) offset in
cpu_alloc()
should give up to PAGE_SIZE alignment for free.