Re: [PATCH bpf-next v2] selftests/bpf: Avoid flaky resize value test for percpu data

On 22/8/26 01:58, Andrii Nakryiko wrote:
> On Tue, Aug 18, 2026 at 6:44 PM Leon Hwang <[email protected]> wrote:
>>
>> On 19/8/26 00:15, [email protected] wrote:
>>>> diff --git a/tools/testing/selftests/bpf/prog_tests/global_data_init.c b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
>>>> index 5671c31085cd..2b69290bcc3e 100644
>>>> --- a/tools/testing/selftests/bpf/prog_tests/global_data_init.c
>>>> +++ b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
>>>
>>> [ ... ]
>>>
>>>> @@ -236,6 +223,57 @@ static void test_global_percpu_data_lskel(void)
>>>>      test_global_percpu_data_lskel__destroy(lskel);
>>>>  }
>>>>
>>>> +#define PAGE_SIZE 4096
>>>> +
>>>> +static void test_global_percpu_data_map_resize(void)
>>>> +{
>>>> +    const __u32 desired_sz = sysconf(_SC_PAGE_SIZE) * 2;
>>>> +    struct test_global_percpu_data *skel;
>>>> +    const int arr_value = -1;
>>>> +    struct bpf_map *map;
>>>> +    int err, prog_fd;
>>>> +    size_t data_sz;
>>>> +
>>>> +    if (sysconf(_SC_PAGE_SIZE) != PAGE_SIZE) {
>>>> +            test__skip();
>>>> +            return;
>>>> +    }
>>>> +
>>>> +    skel = test_global_percpu_data__open();
>>>> +    if (!ASSERT_OK_PTR(skel, "test_global_percpu_data__open"))
>>>> +            return;
>>>> +
>>>> +    map = skel->maps.percpu_arr;
>>>> +    skel->percpu_arr->arr[0] = arr_value;
>>>> +    err = bpf_map__set_value_size(map, desired_sz);
>>>
>>> This isn't a bug, but since the guard above already pins the page size to
>>> 4096, would `const __u32 desired_sz = PAGE_SIZE * 2;` read more directly
>>
>> Will change to 'PAGE_SIZE * 2' if the next revision is needed.
>>
>>> here - and is the unguarded `#define PAGE_SIZE 4096` preferable to the
>>> `#ifndef PAGE_SIZE` form used in sockopt.c?
>>
>> No. PAGE_SIZE must be 4096 here.
>>
> 
> can you please elaborate why do we care about specific PAGE_SIZE
> value? it's a bit weird to guard test based on page size...
> 
It is to verify the mmap change in libbpf's bpf_map_mmap_resize() for
percpu data map, like those subtests in global_map_resize.c.

Thanks,
Leon