linux-kernel - [PATCH v6 1/2] mm: add defines for min/max swappiness

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Message-Id: <20240103164841.2800183-2-schatzberg.dan@gmail.com>
Date: Wed,  3 Jan 2024 08:48:36 -0800
From: Dan Schatzberg <schatzberg.dan@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	linux-mm@...ck.org,
	David Rientjes <rientjes@...gle.com>,
	Chris Li <chrisl@...nel.org>,
	Nhat Pham <nphamcs@...il.com>,
	Tejun Heo <tj@...nel.org>,
	Zefan Li <lizefan.x@...edance.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Jonathan Corbet <corbet@....net>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeelb@...gle.com>,
	Muchun Song <muchun.song@...ux.dev>,
	David Hildenbrand <david@...hat.com>,
	Matthew Wilcox <willy@...radead.org>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Dan Schatzberg <schatzberg.dan@...il.com>,
	Yue Zhao <findns94@...il.com>,
	Yosry Ahmed <yosryahmed@...gle.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: [PATCH v6 1/2] mm: add defines for min/max swappiness

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>
Acked-by: David Rientjes <rientjes@...gle.com>
Acked-by: Chris Li <chrisl@...nel.org>
Reviewed-by: Nhat Pham <nphamcs@...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