Re: [PATCH v2 1/2] memcg: introduce kfuncs for fetching memcg stats

[Yonghong Song <yonghong.song@linux.dev>]

On 10/15/25 4:12 PM, Song Liu wrote:
> On Wed, Oct 15, 2025 at 12:08 PM JP Kobryn <inwardvessel@gmail.com> wrote:
> [...]
>> ---
>>   mm/memcontrol.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 67 insertions(+)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 4deda33625f4..6547c27d4430 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -871,6 +871,73 @@ unsigned long memcg_events_local(struct mem_cgroup *memcg, int event)
>>   }
>>   #endif
>>
>> +static inline struct mem_cgroup *memcg_from_cgroup(struct cgroup *cgrp)
>> +{
>> +       return cgrp ? mem_cgroup_from_css(cgrp->subsys[memory_cgrp_id]) : NULL;
>> +}
>> +
> We should add __bpf_kfunc_start_defs() here, and __bpf_kfunc_end_defs()
> after all the kfuncs.
>
>> +__bpf_kfunc static void memcg_flush_stats(struct cgroup *cgrp)
> We mostly do not make kfunc static, but it seems to also work.

Let us remove 'static' in __bpf_kfunc functions in order to be consistent
with other existing kfuncs.


The __bpf_kfunc macro is
    linux/btf.h:#define __bpf_kfunc __used __retain __noclone noinline

__used and __retain attributes ensure the function won't be removed
by compiler/linker.

>
>> +{
>> +       struct mem_cgroup *memcg = memcg_from_cgroup(cgrp);
>> +
>> +       if (!memcg)
>> +               return;
> Maybe we can let memcg_flush_stats return int, and return -EINVAL
> on memcg == NULL cases?
>
>> +
>> +       mem_cgroup_flush_stats(memcg);
>> +}
>> +
> [...]
>