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

["Sridhar, Kanchana P" <kanchana.p.sridhar@intel.com>]

> -----Original Message-----
> From: Yosry Ahmed <yosryahmed@google.com>
> Sent: Friday, September 27, 2024 8:02 PM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@intel.com>
> Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> hannes@cmpxchg.org; nphamcs@gmail.com; chengming.zhou@linux.dev;
> usamaarif642@gmail.com; shakeel.butt@linux.dev; ryan.roberts@arm.com;
> Huang, Ying <ying.huang@intel.com>; 21cnbao@gmail.com; akpm@linux-
> foundation.org; Zou, Nanhai <nanhai.zou@intel.com>; Feghali, Wajdi K
> <wajdi.k.feghali@intel.com>; Gopal, Vinodh <vinodh.gopal@intel.com>
> Subject: Re: [PATCH v8 4/8] mm: Provide a new count_objcg_events() API for
> batch event updates.
> 
> On Fri, Sep 27, 2024 at 7:16 PM Kanchana P Sridhar
> <kanchana.p.sridhar@intel.com> 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@intel.com>
> > ---
> >  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.

Thanks Yosry. This makes sense. I will incorporate this in v9.

Thanks,
Kanchana

> 
> > +
> >  #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
> >