Re: [External] Re: [PATCH 4/7] mm: memcontrol: simplify lruvec_holds_page_lru_lock

[Muchun Song <songmuchun@bytedance.com>]

On Wed, Apr 14, 2021 at 5:44 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Tue 13-04-21 14:51:50, Muchun Song wrote:
> > We already have a helper lruvec_memcg() to get the memcg from lruvec, we
> > do not need to do it ourselves in the lruvec_holds_page_lru_lock(). So use
> > lruvec_memcg() instead. And if mem_cgroup_disabled() returns false, the
> > page_memcg(page) (the LRU pages) cannot be NULL. So remove the odd logic
> > of "memcg = page_memcg(page) ? : root_mem_cgroup". And use lruvec_pgdat
> > to simplify the code. We can have a single definition for this function
> > that works for !CONFIG_MEMCG, CONFIG_MEMCG + mem_cgroup_disabled() and
> > CONFIG_MEMCG.
>
> Neat. While you are at it wouldn't it make sesne to rename the function
> as well. I do not want to bikeshed but this is really a misnomer. it
> doesn't check anything about locking. page_belongs_lruvec?

Right. lruvec_holds_page_lru_lock is used to check whether
the page belongs to the lruvec. page_belongs_lruvec
obviously more clearer. I can rename it to
page_belongs_lruvec the next version.

>
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > Acked-by: Johannes Weiner <hannes@cmpxchg.org>
>
> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks.

>
> > ---
> >  include/linux/memcontrol.h | 31 +++++++------------------------
> >  1 file changed, 7 insertions(+), 24 deletions(-)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index 4f49865c9958..38b8d3fb24ff 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -755,22 +755,6 @@ static inline struct lruvec *mem_cgroup_page_lruvec(struct page *page)
> >       return mem_cgroup_lruvec(memcg, pgdat);
> >  }
> >
> > -static inline bool lruvec_holds_page_lru_lock(struct page *page,
> > -                                           struct lruvec *lruvec)
> > -{
> > -     pg_data_t *pgdat = page_pgdat(page);
> > -     const struct mem_cgroup *memcg;
> > -     struct mem_cgroup_per_node *mz;
> > -
> > -     if (mem_cgroup_disabled())
> > -             return lruvec == &pgdat->__lruvec;
> > -
> > -     mz = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
> > -     memcg = page_memcg(page) ? : root_mem_cgroup;
> > -
> > -     return lruvec->pgdat == pgdat && mz->memcg == memcg;
> > -}
> > -
> >  struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
> >
> >  struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
> > @@ -1229,14 +1213,6 @@ static inline struct lruvec *mem_cgroup_page_lruvec(struct page *page)
> >       return &pgdat->__lruvec;
> >  }
> >
> > -static inline bool lruvec_holds_page_lru_lock(struct page *page,
> > -                                           struct lruvec *lruvec)
> > -{
> > -     pg_data_t *pgdat = page_pgdat(page);
> > -
> > -     return lruvec == &pgdat->__lruvec;
> > -}
> > -
> >  static inline void lruvec_memcg_debug(struct lruvec *lruvec, struct page *page)
> >  {
> >  }
> > @@ -1518,6 +1494,13 @@ static inline void unlock_page_lruvec_irqrestore(struct lruvec *lruvec,
> >       spin_unlock_irqrestore(&lruvec->lru_lock, flags);
> >  }
> >
> > +static inline bool lruvec_holds_page_lru_lock(struct page *page,
> > +                                           struct lruvec *lruvec)
> > +{
> > +     return lruvec_pgdat(lruvec) == page_pgdat(page) &&
> > +            lruvec_memcg(lruvec) == page_memcg(page);
> > +}
> > +
> >  /* Don't lock again iff page's lruvec locked */
> >  static inline struct lruvec *relock_page_lruvec_irq(struct page *page,
> >               struct lruvec *locked_lruvec)
> > --
> > 2.11.0
>
> --
> Michal Hocko
> SUSE Labs