[PATCH 2/8] mm/mglru: relocate the LRU scan batch limit to callers

[Kairui Song via B4 Relay]

From: Kairui Song <kasong@xxxxxxxxxxx>

Same as active / inactive LRU, MGLRU isolates and scans folios in
batches.  The batch split is done hidden deep in the helper, which
makes the code harder to follow.  The helper's arguments are also
confusing since callers usually request more folios than the batch
size, so the helper almost never processes the full requested amount.

Move the batch splitting into the top loop to make it cleaner, there
should be no behavior change.

Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
 mm/vmscan.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index d7fc7f1fe06d..d48074f9bd87 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4689,10 +4689,10 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	int scanned = 0;
 	int isolated = 0;
 	int skipped = 0;
-	int scan_batch = min(nr_to_scan, MAX_LRU_BATCH);
-	int remaining = scan_batch;
+	unsigned long remaining = nr_to_scan;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
+	VM_WARN_ON_ONCE(nr_to_scan > MAX_LRU_BATCH);
 	VM_WARN_ON_ONCE(!list_empty(list));
 
 	if (get_nr_gens(lruvec, type) == MIN_NR_GENS)
@@ -4745,7 +4745,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 	mod_lruvec_state(lruvec, item, isolated);
 	mod_lruvec_state(lruvec, PGREFILL, sorted);
 	mod_lruvec_state(lruvec, PGSCAN_ANON + type, isolated);
-	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, scan_batch,
+	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
 				scanned, skipped, isolated,
 				type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
 	if (type == LRU_GEN_FILE)
@@ -4827,7 +4827,8 @@ static int isolate_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
 
 		*type_scanned = type;
 
-		scanned = scan_folios(nr_to_scan, lruvec, sc, type, tier, list);
+		scanned = scan_folios(nr_to_scan, lruvec, sc,
+				      type, tier, list);
 		if (scanned)
 			return scanned;
 
@@ -4999,7 +5000,7 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc)
 
 static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 {
-	long nr_to_scan;
+	long nr_batch, nr_to_scan;
 	unsigned long scanned = 0;
 	int swappiness = get_swappiness(lruvec, sc);
 
@@ -5010,7 +5011,8 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 		if (nr_to_scan <= 0)
 			break;
 
-		delta = evict_folios(nr_to_scan, lruvec, sc, swappiness);
+		nr_batch = min(nr_to_scan, MAX_LRU_BATCH);
+		delta = evict_folios(nr_batch, lruvec, sc, swappiness);
 		if (!delta)
 			break;
 
@@ -5615,6 +5617,7 @@ static int run_aging(struct lruvec *lruvec, unsigned long seq,
 static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_control *sc,
 			int swappiness, unsigned long nr_to_reclaim)
 {
+	int nr_batch;
 	DEFINE_MAX_SEQ(lruvec);
 
 	if (seq + MIN_NR_GENS > max_seq)
@@ -5631,8 +5634,8 @@ static int run_eviction(struct lruvec *lruvec, unsigned long seq, struct scan_co
 		if (sc->nr_reclaimed >= nr_to_reclaim)
 			return 0;
 
-		if (!evict_folios(nr_to_reclaim - sc->nr_reclaimed, lruvec, sc,
-				  swappiness))
+		nr_batch = min(nr_to_reclaim - sc->nr_reclaimed, MAX_LRU_BATCH);
+		if (!evict_folios(nr_batch, lruvec, sc, swappiness))
 			return 0;
 
 		cond_resched();

-- 
2.53.0