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

    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

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