Re: [PATCH bpf-next v2 2/7] mm/percpu.c: introduce pcpu_alloc_size()

[Hou Tao <houtao@huaweicloud.com>]

Hi,

On 10/20/2023 12:16 PM, Alexei Starovoitov wrote:
> On Thu, Oct 19, 2023 at 9:09 PM Dennis Zhou <dennis@kernel.org> wrote:
>> On Wed, Oct 18, 2023 at 07:33:38PM +0800, Hou Tao wrote:
>>> From: Hou Tao <houtao1@huawei.com>
>>>
>>> Introduce pcpu_alloc_size() to get the size of the dynamic per-cpu
>>> area. It will be used by bpf memory allocator in the following patches.
>>> BPF memory allocator maintains per-cpu area caches for multiple area
>>> sizes and its free API only has the to-be-freed per-cpu pointer, so it
>>> needs the size of dynamic per-cpu area to select the corresponding cache
>>> when bpf program frees the dynamic per-cpu pointer.
>>>
>>> Signed-off-by: Hou Tao <houtao1@huawei.com>
>>> ---
>>>  include/linux/percpu.h |  1 +
>>>  mm/percpu.c            | 30 ++++++++++++++++++++++++++++++
>>>  2 files changed, 31 insertions(+)
>>>
>>> diff --git a/include/linux/percpu.h b/include/linux/percpu.h
>>> index 68fac2e7cbe6..8c677f185901 100644
>>> --- a/include/linux/percpu.h
>>> +++ b/include/linux/percpu.h
>>> @@ -132,6 +132,7 @@ extern void __init setup_per_cpu_areas(void);
>>>  extern void __percpu *__alloc_percpu_gfp(size_t size, size_t align, gfp_t gfp) __alloc_size(1);
>>>  extern void __percpu *__alloc_percpu(size_t size, size_t align) __alloc_size(1);
>>>  extern void free_percpu(void __percpu *__pdata);
>>> +extern size_t pcpu_alloc_size(void __percpu *__pdata);
>>>
>>>  DEFINE_FREE(free_percpu, void __percpu *, free_percpu(_T))
>>>
>>> diff --git a/mm/percpu.c b/mm/percpu.c
>>> index 76b9c5e63c56..b0cea2dc16a9 100644
>>> --- a/mm/percpu.c
>>> +++ b/mm/percpu.c
>>> @@ -2244,6 +2244,36 @@ static void pcpu_balance_workfn(struct work_struct *work)
>>>       mutex_unlock(&pcpu_alloc_mutex);
>>>  }
>>>
>>> +/**
>>> + * pcpu_alloc_size - the size of the dynamic percpu area
>>> + * @ptr: pointer to the dynamic percpu area
>>> + *
>>> + * Return the size of the dynamic percpu area @ptr.
>>> + *
>> Alexei, can you modify the above comment to:
>>
>> Returns the size of the @ptr allocation.  This is undefined for statically
>> defined percpu variables as there is no corresponding chunk->bound_map.
> Good point! Will do.

I will post v3 to update the API document.

>
> Thanks for the quick review!
>
> .