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References: <20231220152653.3273778-1-schatzberg.dan@gmail.com> <20231220152653.3273778-2-schatzberg.dan@gmail.com>
In-Reply-To: <20231220152653.3273778-2-schatzberg.dan@gmail.com>
From: Nhat Pham <nphamcs@gmail.com>
Date: Wed, 20 Dec 2023 18:01:14 -0800
Message-ID: <CAKEwX=NppvrRFLJzksQ5noHmWHEfWmyiVA2DyhMcY3Lh9dgJ3w@mail.gmail.com>
Subject: Re: [PATCH v5 1/2] mm: add defines for min/max swappiness
To: Dan Schatzberg <schatzberg.dan@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Roman Gushchin <roman.gushchin@linux.dev>, 
	Yosry Ahmed <yosryahmed@google.com>, Huan Yang <link@vivo.com>, linux-kernel@vger.kernel.org, 
	cgroups@vger.kernel.org, linux-mm@kvack.org, Tejun Heo <tj@kernel.org>, 
	Zefan Li <lizefan.x@bytedance.com>, Jonathan Corbet <corbet@lwn.net>, 
	Michal Hocko <mhocko@kernel.org>, Shakeel Butt <shakeelb@google.com>, 
	Muchun Song <muchun.song@linux.dev>, Andrew Morton <akpm@linux-foundation.org>, 
	Kefeng Wang <wangkefeng.wang@huawei.com>, SeongJae Park <sj@kernel.org>, 
	"Vishal Moola (Oracle)" <vishal.moola@gmail.com>, Yue Zhao <findns94@gmail.com>
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On Wed, Dec 20, 2023 at 7:27=E2=80=AFAM Dan Schatzberg <schatzberg.dan@gmai=
l.com> wrote:
>
> We use the constants 0 and 200 in a few places in the mm code when
> referring to the min and max swappiness. This patch adds MIN_SWAPPINESS
> and MAX_SWAPPINESS #defines to improve clarity. There are no functional
> changes.
>
> Signed-off-by: Dan Schatzberg <schatzberg.dan@gmail.com>
> ---
>  include/linux/swap.h |  2 ++
>  mm/memcontrol.c      |  2 +-
>  mm/vmscan.c          | 14 +++++++-------
>  3 files changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index f6dd6575b905..e2ab76c25b4a 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -407,6 +407,8 @@ extern unsigned long try_to_free_pages(struct zonelis=
t *zonelist, int order,
>
>  #define MEMCG_RECLAIM_MAY_SWAP (1 << 1)
>  #define MEMCG_RECLAIM_PROACTIVE (1 << 2)
> +#define MIN_SWAPPINESS 0
> +#define MAX_SWAPPINESS 200
>  extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem=
cg,
>                                                   unsigned long nr_pages,
>                                                   gfp_t gfp_mask,
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b226090fd906..fbe9f02dd206 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4337,7 +4337,7 @@ static int mem_cgroup_swappiness_write(struct cgrou=
p_subsys_state *css,
>  {
>         struct mem_cgroup *memcg =3D mem_cgroup_from_css(css);
>
> -       if (val > 200)
> +       if (val > MAX_SWAPPINESS)
>                 return -EINVAL;
>
>         if (!mem_cgroup_is_root(memcg))
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 9dd8977de5a2..d91963e2d47f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -183,7 +183,7 @@ struct scan_control {
>  #endif
>
>  /*
> - * From 0 .. 200.  Higher means more swappy.
> + * From 0 .. MAX_SWAPPINESS.  Higher means more swappy.
>   */
>  int vm_swappiness =3D 60;
>
> @@ -2403,7 +2403,7 @@ static void get_scan_count(struct lruvec *lruvec, s=
truct scan_control *sc,
>         ap =3D swappiness * (total_cost + 1);
>         ap /=3D anon_cost + 1;
>
> -       fp =3D (200 - swappiness) * (total_cost + 1);
> +       fp =3D (MAX_SWAPPINESS - swappiness) * (total_cost + 1);
>         fp /=3D file_cost + 1;
>
>         fraction[0] =3D ap;
> @@ -4400,7 +4400,7 @@ static int get_type_to_scan(struct lruvec *lruvec, =
int swappiness, int *tier_idx
>  {
>         int type, tier;
>         struct ctrl_pos sp, pv;
> -       int gain[ANON_AND_FILE] =3D { swappiness, 200 - swappiness };
> +       int gain[ANON_AND_FILE] =3D { swappiness, MAX_SWAPPINESS - swappi=
ness };
>
>         /*
>          * Compare the first tier of anon with that of file to determine =
which
> @@ -4436,7 +4436,7 @@ static int isolate_folios(struct lruvec *lruvec, st=
ruct scan_control *sc, int sw
>         /*
>          * Try to make the obvious choice first. When anon and file are b=
oth
>          * available from the same generation, interpret swappiness 1 as =
file
> -        * first and 200 as anon first.
> +        * first and MAX_SWAPPINESS as anon first.
>          */
>         if (!swappiness)
>                 type =3D LRU_GEN_FILE;
> @@ -4444,7 +4444,7 @@ static int isolate_folios(struct lruvec *lruvec, st=
ruct scan_control *sc, int sw
>                 type =3D LRU_GEN_ANON;
>         else if (swappiness =3D=3D 1)
>                 type =3D LRU_GEN_FILE;
> -       else if (swappiness =3D=3D 200)
> +       else if (swappiness =3D=3D MAX_SWAPPINESS)
>                 type =3D LRU_GEN_ANON;
>         else
>                 type =3D get_type_to_scan(lruvec, swappiness, &tier);
> @@ -5398,9 +5398,9 @@ static int run_cmd(char cmd, int memcg_id, int nid,=
 unsigned long seq,
>
>         lruvec =3D get_lruvec(memcg, nid);
>
> -       if (swappiness < 0)
> +       if (swappiness < MIN_SWAPPINESS)
>                 swappiness =3D get_swappiness(lruvec, sc);
> -       else if (swappiness > 200)
> +       else if (swappiness > MAX_SWAPPINESS)
>                 goto done;
>
>         switch (cmd) {
> --
> 2.39.3
>

Sorry for being late to the party :) Was preoccupied with zswap convos.

Hmm these are all the occurrences of 0 and 200 (in the context of
swappiness) I can dig out. So, FWIW:
Reviewed-by: Nhat Pham <nphamcs@gmail.com>