[PATCH 5/7] mm/mglru: use explicit tier range in read_ctrl_pos()
From: Kairui Song via B4 Relay
Date: Tue Aug 18 2026 - 01:41:18 EST
From: Kairui Song <kasong@xxxxxxxxxxx>
read_ctrl_pos() encodes the tier range in a single "tier" parameter
via "tier % MAX_NR_TIERS" as the start and "min(tier, MAX_NR_TIERS-1)"
as the end. This is hard to follow, maintain, or extend. Tier values
0..3 select a single tier, while tier == MAX_NR_TIERS selects the
full range.
Replace it with explicit (tier_min, tier_max) parameters using a
closed [tier_min, tier_max] interval, and add LRU_TIER_MIN and
LRU_TIER_MAX for the tier bounds. The call sites now become
self-documenting:
- get_tier_idx: (LRU_TIER_MIN, LRU_TIER_MIN) for the first tier,
(tier, tier) for each subsequent tier
- get_type_to_scan: (LRU_TIER_MIN, LRU_TIER_MAX) for the full range
No functional change.
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
include/linux/mmzone.h | 2 ++
mm/vmscan.c | 18 ++++++++++--------
2 files changed, 12 insertions(+), 8 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 32d9354a754f..d0b5c6217d25 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -492,6 +492,8 @@ enum lruvec_flags {
* folio->flags, masked by LRU_REFS_MASK.
*/
#define MAX_NR_TIERS 4U
+#define LRU_TIER_MIN 0U
+#define LRU_TIER_MAX (MAX_NR_TIERS - 1)
#ifndef __GENERATING_BOUNDS_H
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a819be6b7ae9..a613bb8d7271 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3198,8 +3198,8 @@ struct ctrl_pos {
int gain;
};
-static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain,
- struct ctrl_pos *pos)
+static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier_min,
+ int tier_max, int gain, struct ctrl_pos *pos)
{
int i;
struct lru_gen_folio *lrugen = &lruvec->lrugen;
@@ -3208,7 +3208,7 @@ static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain,
pos->gain = gain;
pos->refaulted = pos->total = 0;
- for (i = tier % MAX_NR_TIERS; i <= min(tier, MAX_NR_TIERS - 1); i++) {
+ for (i = tier_min; i <= tier_max; i++) {
pos->refaulted += lrugen->avg_refaulted[type][i] +
atomic_long_read(&lrugen->refaulted[hist][type][i]);
pos->total += lrugen->avg_total[type][i] +
@@ -4804,9 +4804,9 @@ static int get_tier_idx(struct lruvec *lruvec, int type)
* This value is chosen because any other tier would have at least twice
* as many refaults as the first tier.
*/
- read_ctrl_pos(lruvec, type, 0, 2, &sp);
- for (tier = 1; tier < MAX_NR_TIERS; tier++) {
- read_ctrl_pos(lruvec, type, tier, 3, &pv);
+ read_ctrl_pos(lruvec, type, LRU_TIER_MIN, LRU_TIER_MIN, 2, &sp);
+ for (tier = LRU_TIER_MIN + 1; tier <= LRU_TIER_MAX; tier++) {
+ read_ctrl_pos(lruvec, type, tier, tier, 3, &pv);
if (!positive_ctrl_err(&sp, &pv))
break;
}
@@ -4827,8 +4827,10 @@ static int get_type_to_scan(struct lruvec *lruvec, int swappiness)
* Compare the sum of all tiers of anon with that of file to determine
* which type to scan.
*/
- read_ctrl_pos(lruvec, LRU_GEN_ANON, MAX_NR_TIERS, swappiness, &sp);
- read_ctrl_pos(lruvec, LRU_GEN_FILE, MAX_NR_TIERS, MAX_SWAPPINESS - swappiness, &pv);
+ read_ctrl_pos(lruvec, LRU_GEN_ANON, LRU_TIER_MIN, LRU_TIER_MAX,
+ swappiness, &sp);
+ read_ctrl_pos(lruvec, LRU_GEN_FILE, LRU_TIER_MIN, LRU_TIER_MAX,
+ MAX_SWAPPINESS - swappiness, &pv);
return positive_ctrl_err(&sp, &pv);
}
--
2.55.0