[PATCH RFC 06/15] mm/mglru: use explicit tier range in read_ctrl_pos()
From: Kairui Song via B4 Relay
Date: Mon Aug 03 2026 - 15:58:07 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 or 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
half-open [tier_min, tier_max) interval, which is the conventional C
idiom. The call sites become self-documenting:
- get_tier_idx: (0, 1) for tier 0, (tier, tier+1) for each tier
- get_type_to_scan: (0, MAX_NR_TIERS) for the full range
No functional change.
Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
mm/vmscan.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c2ea92c2b69e..a359d5a1ff41 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3192,8 +3192,8 @@ 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;
@@ -3202,7 +3202,7 @@ 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] +
@@ -4805,9 +4805,9 @@ 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);
+ read_ctrl_pos(lruvec, type, 0, 1, 2, &sp);
for (tier = 1; tier < MAX_NR_TIERS; tier++) {
- read_ctrl_pos(lruvec, type, tier, 3, &pv);
+ read_ctrl_pos(lruvec, type, tier, tier + 1, 3, &pv);
if (!positive_ctrl_err(&sp, &pv))
break;
}
@@ -4828,8 +4828,8 @@ 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, 0, MAX_NR_TIERS, swappiness, &sp);
+ read_ctrl_pos(lruvec, LRU_GEN_FILE, 0, MAX_NR_TIERS, MAX_SWAPPINESS - swappiness, &pv);
return positive_ctrl_err(&sp, &pv);
}
--
2.55.0