Re: [External] Re: [PATCH v2 1/5] mm: memcontrol: introduce obj_cgroup_{un}charge_page

[Muchun Song <songmuchun@bytedance.com>]

On Sat, Mar 6, 2021 at 2:56 AM Roman Gushchin <guro@fb.com> wrote:
>
> On Wed, Mar 03, 2021 at 01:59:13PM +0800, Muchun Song wrote:
> > We know that the unit of slab object charging is bytes, the unit of
> > kmem page charging is PAGE_SIZE. If we want to reuse obj_cgroup APIs
> > to charge the kmem pages, we should pass PAGE_SIZE (as third parameter)
> > to obj_cgroup_charge(). Because the size is already PAGE_SIZE, we can
> > skip touch the objcg stock. And obj_cgroup_{un}charge_page() are
> > introduced to charge in units of page level.
> >
> > In the later patch, we also can reuse those two helpers to charge or
> > uncharge a number of kernel pages to a object cgroup. This is just
> > a code movement without any functional changes.
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>
> This patch looks good to me, even as a standalone refactoring.
> Please, rename obj_cgroup_charge_page() to obj_cgroup_charge_pages()
> and the same with uncharge. It's because _page suffix usually means
> we're dealing with a physical page (e.g. struct page * as an argument),
> here it's not the case.

Make sense.

>
> Please, add my Acked-by: Roman Gushchin <guro@fb.com>
> after the renaming.

Will do. Thanks for your review.

>
> Thank you!
>
> > ---
> >  mm/memcontrol.c | 46 +++++++++++++++++++++++++++++++---------------
> >  1 file changed, 31 insertions(+), 15 deletions(-)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 845eec01ef9d..faae16def127 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -3056,6 +3056,34 @@ static void memcg_free_cache_id(int id)
> >       ida_simple_remove(&memcg_cache_ida, id);
> >  }
> >
> > +static inline void obj_cgroup_uncharge_page(struct obj_cgroup *objcg,
> > +                                         unsigned int nr_pages)
> > +{
> > +     rcu_read_lock();
> > +     __memcg_kmem_uncharge(obj_cgroup_memcg(objcg), nr_pages);
> > +     rcu_read_unlock();
> > +}
> > +
> > +static int obj_cgroup_charge_page(struct obj_cgroup *objcg, gfp_t gfp,
> > +                               unsigned int nr_pages)
> > +{
> > +     struct mem_cgroup *memcg;
> > +     int ret;
> > +
> > +     rcu_read_lock();
> > +retry:
> > +     memcg = obj_cgroup_memcg(objcg);
> > +     if (unlikely(!css_tryget(&memcg->css)))
> > +             goto retry;
> > +     rcu_read_unlock();
> > +
> > +     ret = __memcg_kmem_charge(memcg, gfp, nr_pages);
> > +
> > +     css_put(&memcg->css);
> > +
> > +     return ret;
> > +}
> > +
> >  /**
> >   * __memcg_kmem_charge: charge a number of kernel pages to a memcg
> >   * @memcg: memory cgroup to charge
> > @@ -3180,11 +3208,8 @@ static void drain_obj_stock(struct memcg_stock_pcp *stock)
> >               unsigned int nr_pages = stock->nr_bytes >> PAGE_SHIFT;
> >               unsigned int nr_bytes = stock->nr_bytes & (PAGE_SIZE - 1);
> >
> > -             if (nr_pages) {
> > -                     rcu_read_lock();
> > -                     __memcg_kmem_uncharge(obj_cgroup_memcg(old), nr_pages);
> > -                     rcu_read_unlock();
> > -             }
> > +             if (nr_pages)
> > +                     obj_cgroup_uncharge_page(old, nr_pages);
> >
> >               /*
> >                * The leftover is flushed to the centralized per-memcg value.
> > @@ -3242,7 +3267,6 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
> >
> >  int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size)
> >  {
> > -     struct mem_cgroup *memcg;
> >       unsigned int nr_pages, nr_bytes;
> >       int ret;
> >
> > @@ -3259,24 +3283,16 @@ int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size)
> >        * refill_obj_stock(), called from this function or
> >        * independently later.
> >        */
> > -     rcu_read_lock();
> > -retry:
> > -     memcg = obj_cgroup_memcg(objcg);
> > -     if (unlikely(!css_tryget(&memcg->css)))
> > -             goto retry;
> > -     rcu_read_unlock();
> > -
> >       nr_pages = size >> PAGE_SHIFT;
> >       nr_bytes = size & (PAGE_SIZE - 1);
> >
> >       if (nr_bytes)
> >               nr_pages += 1;
> >
> > -     ret = __memcg_kmem_charge(memcg, gfp, nr_pages);
> > +     ret = obj_cgroup_charge_page(objcg, gfp, nr_pages);
> >       if (!ret && nr_bytes)
> >               refill_obj_stock(objcg, PAGE_SIZE - nr_bytes);
> >
> > -     css_put(&memcg->css);
> >       return ret;
> >  }
> >
> > --
> > 2.11.0
> >