Re: [External] [PATCH v3 2/3] mm, memcg: inline mem_cgroup_{charge/uncharge} to improve disabled memcg config

[Muchun Song <songmuchun@bytedance.com>]

On Sat, Jul 10, 2021 at 8:36 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> Inline mem_cgroup_{charge/uncharge} and mem_cgroup_uncharge_list functions
> functions to perform mem_cgroup_disabled static key check inline before
> calling the main body of the function. This minimizes the memcg overhead
> in the pagefault and exit_mmap paths when memcgs are disabled using
> cgroup_disable=memory command-line option.
> This change results in ~0.4% overhead reduction when running PFT test
> comparing {CONFIG_MEMCG=n} against {CONFIG_MEMCG=y, cgroup_disable=memory}
> configurationon on an 8-core ARM64 Android device.
>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

But some nits below.

> ---
>  include/linux/memcontrol.h | 28 +++++++++++++++++++++++++---
>  mm/memcontrol.c            | 29 ++++++++++-------------------
>  2 files changed, 35 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index bfe5c486f4ad..39fa88051a42 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -693,13 +693,35 @@ static inline bool mem_cgroup_below_min(struct mem_cgroup *memcg)
>                 page_counter_read(&memcg->memory);
>  }
>
> -int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask);
> +int __mem_cgroup_charge(struct page *page, struct mm_struct *mm,
> +                       gfp_t gfp_mask);
> +static inline int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
> +                                   gfp_t gfp_mask)
> +{
> +       if (mem_cgroup_disabled())
> +               return 0;
> +       return __mem_cgroup_charge(page, mm, gfp_mask);
> +}
> +
>  int mem_cgroup_swapin_charge_page(struct page *page, struct mm_struct *mm,
>                                   gfp_t gfp, swp_entry_t entry);
>  void mem_cgroup_swapin_uncharge_swap(swp_entry_t entry);
>
> -void mem_cgroup_uncharge(struct page *page);
> -void mem_cgroup_uncharge_list(struct list_head *page_list);
> +void __mem_cgroup_uncharge(struct page *page);
> +static inline void mem_cgroup_uncharge(struct page *page)
> +{
> +       if (mem_cgroup_disabled())
> +               return;
> +       __mem_cgroup_uncharge(page);
> +}
> +
> +void __mem_cgroup_uncharge_list(struct list_head *page_list);
> +static inline void mem_cgroup_uncharge_list(struct list_head *page_list)
> +{
> +       if (mem_cgroup_disabled())
> +               return;
> +       __mem_cgroup_uncharge_list(page_list);
> +}
>
>  void mem_cgroup_migrate(struct page *oldpage, struct page *newpage);
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a228cd51c4bd..cdaf7003b43d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6701,8 +6701,7 @@ void mem_cgroup_calculate_protection(struct mem_cgroup *root,
>                         atomic_long_read(&parent->memory.children_low_usage)));
>  }
>
> -static int __mem_cgroup_charge(struct page *page, struct mem_cgroup *memcg,
> -                              gfp_t gfp)
> +static int charge_memcg(struct page *page, struct mem_cgroup *memcg, gfp_t gfp)
>  {
>         unsigned int nr_pages = thp_nr_pages(page);
>         int ret;
> @@ -6723,7 +6722,7 @@ static int __mem_cgroup_charge(struct page *page, struct mem_cgroup *memcg,
>  }
>
>  /**
> - * mem_cgroup_charge - charge a newly allocated page to a cgroup
> + * __mem_cgroup_charge - charge a newly allocated page to a cgroup
>   * @page: page to charge
>   * @mm: mm context of the victim
>   * @gfp_mask: reclaim mode
> @@ -6736,16 +6735,14 @@ static int __mem_cgroup_charge(struct page *page, struct mem_cgroup *memcg,
>   *
>   * Returns 0 on success. Otherwise, an error code is returned.
>   */
> -int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
> +int __mem_cgroup_charge(struct page *page, struct mm_struct *mm,
> +                       gfp_t gfp_mask)
>  {
>         struct mem_cgroup *memcg;
>         int ret;
>
> -       if (mem_cgroup_disabled())
> -               return 0;
> -
>         memcg = get_mem_cgroup_from_mm(mm);
> -       ret = __mem_cgroup_charge(page, memcg, gfp_mask);
> +       ret = charge_memcg(page, memcg, gfp_mask);
>         css_put(&memcg->css);
>
>         return ret;
> @@ -6780,7 +6777,7 @@ int mem_cgroup_swapin_charge_page(struct page *page, struct mm_struct *mm,
>                 memcg = get_mem_cgroup_from_mm(mm);
>         rcu_read_unlock();
>
> -       ret = __mem_cgroup_charge(page, memcg, gfp);
> +       ret = charge_memcg(page, memcg, gfp);
>
>         css_put(&memcg->css);
>         return ret;
> @@ -6916,18 +6913,15 @@ static void uncharge_page(struct page *page, struct uncharge_gather *ug)
>  }
>
>  /**
> - * mem_cgroup_uncharge - uncharge a page
> + * __mem_cgroup_uncharge - uncharge a page
>   * @page: page to uncharge
>   *
>   * Uncharge a page previously charged with mem_cgroup_charge().

The comment here also needs to be updated.

mem_cgroup_uncharge() -> __mem_cgroup_uncharge()

>   */
> -void mem_cgroup_uncharge(struct page *page)
> +void __mem_cgroup_uncharge(struct page *page)
>  {
>         struct uncharge_gather ug;
>
> -       if (mem_cgroup_disabled())
> -               return;
> -
>         /* Don't touch page->lru of any random page, pre-check: */
>         if (!page_memcg(page))
>                 return;
> @@ -6938,20 +6932,17 @@ void mem_cgroup_uncharge(struct page *page)
>  }
>
>  /**
> - * mem_cgroup_uncharge_list - uncharge a list of page
> + * __mem_cgroup_uncharge_list - uncharge a list of page
>   * @page_list: list of pages to uncharge
>   *
>   * Uncharge a list of pages previously charged with
>   * mem_cgroup_charge().

Should be __mem_cgroup_charge().

Thanks.

>   */
> -void mem_cgroup_uncharge_list(struct list_head *page_list)
> +void __mem_cgroup_uncharge_list(struct list_head *page_list)
>  {
>         struct uncharge_gather ug;
>         struct page *page;
>
> -       if (mem_cgroup_disabled())
> -               return;
> -
>         uncharge_gather_clear(&ug);
>         list_for_each_entry(page, page_list, lru)
>                 uncharge_page(page, &ug);
> --
> 2.32.0.93.g670b81a890-goog
>