On Sat, Mar 6, 2021 at 2:56 AM Roman Gushchin <guro@xxxxxx> 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@xxxxxxxxxxxxx>
>
> 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@xxxxxx>
> 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
> >
