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

[Yonghong Song]

On 10/15/25 4:12 PM, Song Liu wrote:
> On Wed, Oct 15, 2025 at 12:08 PM JP Kobryn <inwardvessel@xxxxxxxxx> 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);
> > +}
> > +
> [...]