linux-kernel - Re: [PATCH v5 1/2] mm: add defines for min/max swappiness

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Date: Wed, 20 Dec 2023 18:01:14 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Dan Schatzberg <schatzberg.dan@...il.com>
Cc: Johannes Weiner <hannes@...xchg.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Yosry Ahmed <yosryahmed@...gle.com>, Huan Yang <link@...o.com>, linux-kernel@...r.kernel.org, 
	cgroups@...r.kernel.org, linux-mm@...ck.org, Tejun Heo <tj@...nel.org>, 
	Zefan Li <lizefan.x@...edance.com>, Jonathan Corbet <corbet@....net>, 
	Michal Hocko <mhocko@...nel.org>, Shakeel Butt <shakeelb@...gle.com>, 
	Muchun Song <muchun.song@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
	Kefeng Wang <wangkefeng.wang@...wei.com>, SeongJae Park <sj@...nel.org>, 
	"Vishal Moola (Oracle)" <vishal.moola@...il.com>, Yue Zhao <findns94@...il.com>
Subject: Re: [PATCH v5 1/2] mm: add defines for min/max swappiness

On Wed, Dec 20, 2023 at 7:27 AM Dan Schatzberg <schatzberg.dan@...il.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@...il.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 zonelist *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 *memcg,
>                                                   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 cgroup_subsys_state *css,
>  {
>         struct mem_cgroup *memcg = 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 = 60;
>
> @@ -2403,7 +2403,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>         ap = swappiness * (total_cost + 1);
>         ap /= anon_cost + 1;
>
> -       fp = (200 - swappiness) * (total_cost + 1);
> +       fp = (MAX_SWAPPINESS - swappiness) * (total_cost + 1);
>         fp /= file_cost + 1;
>
>         fraction[0] = 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] = { swappiness, 200 - swappiness };
> +       int gain[ANON_AND_FILE] = { swappiness, MAX_SWAPPINESS - swappiness };
>
>         /*
>          * Compare the first tier of anon with that of file to determine which
> @@ -4436,7 +4436,7 @@ static int isolate_folios(struct lruvec *lruvec, struct scan_control *sc, int sw
>         /*
>          * Try to make the obvious choice first. When anon and file are both
>          * 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 = LRU_GEN_FILE;
> @@ -4444,7 +4444,7 @@ static int isolate_folios(struct lruvec *lruvec, struct scan_control *sc, int sw
>                 type = LRU_GEN_ANON;
>         else if (swappiness == 1)
>                 type = LRU_GEN_FILE;
> -       else if (swappiness == 200)
> +       else if (swappiness == MAX_SWAPPINESS)
>                 type = LRU_GEN_ANON;
>         else
>                 type = 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 = get_lruvec(memcg, nid);
>
> -       if (swappiness < 0)
> +       if (swappiness < MIN_SWAPPINESS)
>                 swappiness = 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@...il.com>