Re: [PATCH v8 4/8] mm: Provide a new count_objcg_events() API for batch event updates.

[Chengming Zhou]

On 2024/9/28 11:02, Yosry Ahmed wrote:
> On Fri, Sep 27, 2024 at 7:16 PM Kanchana P Sridhar
> <kanchana.p.sridhar@xxxxxxxxx> wrote:
> > With the introduction of zswap_store() swapping out large folios,
> > we need to efficiently update the objcg's memcg events once per
> > successfully stored folio. For instance, the 'ZSWPOUT' event needs
> > to be incremented by folio_nr_pages().
> >
> > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>
> > ---
> >   include/linux/memcontrol.h | 20 ++++++++++++++++++++
> >   1 file changed, 20 insertions(+)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index 15c2716f9aa3..f47fd00c5eea 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -1778,6 +1778,21 @@ static inline void count_objcg_event(struct obj_cgroup *objcg,
> >          rcu_read_unlock();
> >   }
> >
> > +static inline void count_objcg_events(struct obj_cgroup *objcg,
> > +                                     enum vm_event_item idx,
> > +                                     unsigned long count)
> > +{
> > +       struct mem_cgroup *memcg;
> > +
> > +       if (!memcg_kmem_online())
> > +               return;
> > +
> > +       rcu_read_lock();
> > +       memcg = obj_cgroup_memcg(objcg);
> > +       count_memcg_events(memcg, idx, count);
> > +       rcu_read_unlock();
> > +}
>
> Instead of replicating the code in count_objcg_event(), we should
> change count_objcg_event() to become count_objcg_events() (i.e. add a
> count parameter). The existing callers can pass in 1, there's only 3
> of them anyway (2 after patch 6), and they are all in zswap.

Right, agree.

> > +
> >   #else
> >   static inline bool mem_cgroup_kmem_disabled(void)
> >   {
> > @@ -1834,6 +1849,11 @@ static inline void count_objcg_event(struct obj_cgroup *objcg,
> >   {
> >   }
> >
> > +static inline void count_objcg_events(struct obj_cgroup *objcg,
> > +                                     enum vm_event_item idx,
> > +                                     unsigned long count)
> > +{
> > +}
> >   #endif /* CONFIG_MEMCG */
> >
> >   #if defined(CONFIG_MEMCG) && defined(CONFIG_ZSWAP)
> > --
> > 2.27.0