Re: [PATCH v3 3/3] mm, memcg: inline swap-related functions to improve disabled memcg config

[Suren Baghdasaryan <surenb@google.com>]

On Mon, Jul 12, 2021 at 12:17 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Fri 09-07-21 17:36:26, Suren Baghdasaryan wrote:
> > Inline mem_cgroup_try_charge_swap, mem_cgroup_uncharge_swap and
> > cgroup_throttle_swaprate 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 ~1% overhead reduction when running PFT test
> > comparing {CONFIG_MEMCG=n} against {CONFIG_MEMCG=y, cgroup_disable=memory}
> > configuration on an 8-core ARM64 Android device.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > Reviewed-by: Shakeel Butt <shakeelb@google.com>
> > Acked-by: Johannes Weiner <hannes@cmpxchg.org>
>
> I find it a bit surprising to see such a big difference over a function
> call in a slow path like swap in/out.

Might be due to the nature of the test. It is designed to generate an
avalanche of anonymous pagefaults and that might be the reason swap
functions are hit this hard.

>
> Anyway the change makes sense.
>
> Acked-by: Michal Hocko <mhocko@suse.com>
>
> Thanks!
>
> > ---
> >  include/linux/swap.h | 26 +++++++++++++++++++++++---
> >  mm/memcontrol.c      | 14 ++++----------
> >  mm/swapfile.c        |  5 +----
> >  3 files changed, 28 insertions(+), 17 deletions(-)
> >
> > diff --git a/include/linux/swap.h b/include/linux/swap.h
> > index 6f5a43251593..f30d26b0f71d 100644
> > --- a/include/linux/swap.h
> > +++ b/include/linux/swap.h
> > @@ -721,7 +721,13 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
> >  #endif
> >
> >  #if defined(CONFIG_SWAP) && defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
> > -extern void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask);
> > +extern void __cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask);
> > +static inline  void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
> > +{
> > +     if (mem_cgroup_disabled())
> > +             return;
> > +     __cgroup_throttle_swaprate(page, gfp_mask);
> > +}
> >  #else
> >  static inline void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
> >  {
> > @@ -730,8 +736,22 @@ static inline void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
> >
> >  #ifdef CONFIG_MEMCG_SWAP
> >  extern void mem_cgroup_swapout(struct page *page, swp_entry_t entry);
> > -extern int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry);
> > -extern void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages);
> > +extern int __mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry);
> > +static inline int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
> > +{
> > +     if (mem_cgroup_disabled())
> > +             return 0;
> > +     return __mem_cgroup_try_charge_swap(page, entry);
> > +}
> > +
> > +extern void __mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages);
> > +static inline void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
> > +{
> > +     if (mem_cgroup_disabled())
> > +             return;
> > +     __mem_cgroup_uncharge_swap(entry, nr_pages);
> > +}
> > +
> >  extern long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg);
> >  extern bool mem_cgroup_swap_full(struct page *page);
> >  #else
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index cdaf7003b43d..0b05322836ec 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -7234,7 +7234,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
> >  }
> >
> >  /**
> > - * mem_cgroup_try_charge_swap - try charging swap space for a page
> > + * __mem_cgroup_try_charge_swap - try charging swap space for a page
> >   * @page: page being added to swap
> >   * @entry: swap entry to charge
> >   *
> > @@ -7242,16 +7242,13 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
> >   *
> >   * Returns 0 on success, -ENOMEM on failure.
> >   */
> > -int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
> > +int __mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
> >  {
> >       unsigned int nr_pages = thp_nr_pages(page);
> >       struct page_counter *counter;
> >       struct mem_cgroup *memcg;
> >       unsigned short oldid;
> >
> > -     if (mem_cgroup_disabled())
> > -             return 0;
> > -
> >       if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
> >               return 0;
> >
> > @@ -7287,18 +7284,15 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
> >  }
> >
> >  /**
> > - * mem_cgroup_uncharge_swap - uncharge swap space
> > + * __mem_cgroup_uncharge_swap - uncharge swap space
> >   * @entry: swap entry to uncharge
> >   * @nr_pages: the amount of swap space to uncharge
> >   */
> > -void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
> > +void __mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
> >  {
> >       struct mem_cgroup *memcg;
> >       unsigned short id;
> >
> > -     if (mem_cgroup_disabled())
> > -             return;
> > -
> >       id = swap_cgroup_record(entry, 0, nr_pages);
> >       rcu_read_lock();
> >       memcg = mem_cgroup_from_id(id);
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 707fa0481bb4..04a0c83f1313 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -3773,14 +3773,11 @@ static void free_swap_count_continuations(struct swap_info_struct *si)
> >  }
> >
> >  #if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
> > -void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
> > +void __cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
> >  {
> >       struct swap_info_struct *si, *next;
> >       int nid = page_to_nid(page);
> >
> > -     if (mem_cgroup_disabled())
> > -             return;
> > -
> >       if (!(gfp_mask & __GFP_IO))
> >               return;
> >
> > --
> > 2.32.0.93.g670b81a890-goog
>
> --
> Michal Hocko
> SUSE Labs