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From:   Suren Baghdasaryan <surenb@google.com>
Date:   Wed, 20 Apr 2022 16:34:59 -0700
Message-ID: <CAJuCfpFMgLvLHKK8ZKrU3vciZFK0FJoCFen_3tbUBk5s+yWnSw@mail.gmail.com>
Subject: Re: [PATCH v2] mm/damon: Fix the timer always stays active
To:     Hailong Tu <tuhailong@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, sj@kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@google.com>,
        linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, tuhailong@oppo.com,
        lichunpeng@oppo.com
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On Wed, Apr 20, 2022 at 3:46 PM Hailong Tu <tuhailong@gmail.com> wrote:
>
> The timer stays active even if the reclaim mechanism is never enabled.
> It is unnecessary overhead can be completely avoided by using module_param_call() for enabled flag.
>
> Signed-off-by: Hailong Tu <tuhailong@gmail.com>
> ---
>  mm/damon/reclaim.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
> index e34c4d0c4d93..389c4be4f62b 100644
> --- a/mm/damon/reclaim.c
> +++ b/mm/damon/reclaim.c
> @@ -28,7 +28,6 @@
>   * this.
>   */
>  static bool enabled __read_mostly;
> -module_param(enabled, bool, 0600);
>
>  /*
>   * Time threshold for cold memory regions identification in microseconds.
> @@ -358,11 +357,32 @@ static void damon_reclaim_timer_fn(struct work_struct *work)
>                         enabled = last_enabled;
>         }
>
> -       schedule_delayed_work(&damon_reclaim_timer,
> +       if (enabled)
> +               schedule_delayed_work(&damon_reclaim_timer,
>                         msecs_to_jiffies(ENABLE_CHECK_INTERVAL_MS));
>  }
>  static DECLARE_DELAYED_WORK(damon_reclaim_timer, damon_reclaim_timer_fn);
>
> +static int enabled_show(char *buffer, const struct kernel_param *kp)
> +{
> +       return sprintf(buffer, "%c\n", enabled ? 'Y' : 'N');
> +}
> +
> +static int enabled_store(const char *val,
> +               const struct kernel_param *kp)
> +{
> +       int rc = param_set_bool(val, kp);
> +
> +       if (rc < 0)
> +               return rc;
> +
> +       if (enabled)
> +               schedule_delayed_work(&damon_reclaim_timer, 0);
> +
> +       return 0;
> +}
> +module_param_call(enabled, enabled_store, enabled_show, &enabled, 0600);

As Matthew pointed out in the previous version, you can use
param_get_bool instead of enabled_show here.

> +
>  static int damon_reclaim_after_aggregation(struct damon_ctx *c)
>  {
>         struct damos *s;
> --
> 2.25.1
>