Re: [PATCH 1/2 v3] memcg: rename do_flush_stats and add force flag

[Yosry Ahmed <yosryahmed@google.com>]

On Mon, Oct 28, 2024 at 7:11 PM JP Kobryn <inwardvessel@gmail.com> wrote:
>
> Change the name to something more consistent with others in the file and
> use double unders to signify it is associated with the
> mem_cgroup_flush_stats() API call. Additionally include a new flag that
> call sites use to indicate a forced flush; skipping checks and flushing
> unconditionally. There are no changes in functionality.
>
> Signed-off-by: JP Kobryn <inwardvessel@gmail.com>

Reviewed-by: Yosry Ahmed <yosryahmed@google.com>

> ---
>  mm/memcontrol.c | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 18c3f513d766..59f6f247fc13 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -588,8 +588,11 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val)
>         }
>  }
>
> -static void do_flush_stats(struct mem_cgroup *memcg)
> +static void __mem_cgroup_flush_stats(struct mem_cgroup *memcg, bool force)
>  {
> +       if (!force && !memcg_vmstats_needs_flush(memcg->vmstats))
> +               return;
> +
>         if (mem_cgroup_is_root(memcg))
>                 WRITE_ONCE(flush_last_time, jiffies_64);
>
> @@ -613,8 +616,7 @@ void mem_cgroup_flush_stats(struct mem_cgroup *memcg)
>         if (!memcg)
>                 memcg = root_mem_cgroup;
>
> -       if (memcg_vmstats_needs_flush(memcg->vmstats))
> -               do_flush_stats(memcg);
> +       __mem_cgroup_flush_stats(memcg, false);
>  }
>
>  void mem_cgroup_flush_stats_ratelimited(struct mem_cgroup *memcg)
> @@ -630,7 +632,7 @@ static void flush_memcg_stats_dwork(struct work_struct *w)
>          * Deliberately ignore memcg_vmstats_needs_flush() here so that flushing
>          * in latency-sensitive paths is as cheap as possible.
>          */
> -       do_flush_stats(root_mem_cgroup);
> +       __mem_cgroup_flush_stats(root_mem_cgroup, true);
>         queue_delayed_work(system_unbound_wq, &stats_flush_dwork, FLUSH_TIME);
>  }
>
> @@ -5281,11 +5283,8 @@ bool obj_cgroup_may_zswap(struct obj_cgroup *objcg)
>                         break;
>                 }
>
> -               /*
> -                * mem_cgroup_flush_stats() ignores small changes. Use
> -                * do_flush_stats() directly to get accurate stats for charging.
> -                */
> -               do_flush_stats(memcg);
> +               /* Force flush to get accurate stats for charging */
> +               __mem_cgroup_flush_stats(memcg, true);
>                 pages = memcg_page_state(memcg, MEMCG_ZSWAP_B) / PAGE_SIZE;
>                 if (pages < max)
>                         continue;
> --
> 2.47.0
>