[PATCH RFC] mm: mglru: provide a separate list for lazyfree anon folios

[Barry Song <21cnbao@gmail.com>]

From: Barry Song <v-songbaohua@oppo.com>

This follows up on the discussion regarding Gaoxu's work[1]. It's
unclear if there's still interest in implementing a separate LRU
list for lazyfree folios, but I decided to explore it out of
curiosity.

According to Lokesh, MADV_FREE'd anon folios are expected to be 
released earlier than file folios. One option, as implemented 
by Gao Xu, is to place lazyfree anon folios at the tail of the 
file's `min_seq` generation. However, this approach results in 
lazyfree folios being released in a LIFO manner, which conflicts 
with LRU behavior, as noted by Michal.

To address this, this patch proposes maintaining a separate list 
for lazyfree anon folios while keeping them classified under the 
"file" LRU type to minimize code changes. These lazyfree anon 
folios will still be counted as file folios and share the same 
generation with regular files. In the eviction path, the lazyfree 
list will be prioritized for scanning before the actual file 
LRU list.

[1] https://lore.kernel.org/linux-mm/f29f64e29c08427b95e3df30a5770056@honor.com/

Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 include/linux/mm_inline.h |  5 +-
 include/linux/mmzone.h    |  2 +-
 mm/vmscan.c               | 97 +++++++++++++++++++++++----------------
 3 files changed, 61 insertions(+), 43 deletions(-)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index f4fe593c1400..118d70ed3120 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -225,6 +225,7 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
 	int gen = folio_lru_gen(folio);
 	int type = folio_is_file_lru(folio);
 	int zone = folio_zonenum(folio);
+	int lazyfree = type ? folio_test_anon(folio) : 0;
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	VM_WARN_ON_ONCE_FOLIO(gen != -1, folio);
@@ -262,9 +263,9 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
 	lru_gen_update_size(lruvec, folio, -1, gen);
 	/* for folio_rotate_reclaimable() */
 	if (reclaiming)
-		list_add_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
+		list_add_tail(&folio->lru, &lrugen->folios[gen][type + lazyfree][zone]);
 	else
-		list_add(&folio->lru, &lrugen->folios[gen][type][zone]);
+		list_add(&folio->lru, &lrugen->folios[gen][type + lazyfree][zone]);
 
 	return true;
 }
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 17506e4a2835..5d2331778528 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -434,7 +434,7 @@ struct lru_gen_folio {
 	/* the birth time of each generation in jiffies */
 	unsigned long timestamps[MAX_NR_GENS];
 	/* the multi-gen LRU lists, lazily sorted on eviction */
-	struct list_head folios[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
+	struct list_head folios[MAX_NR_GENS][ANON_AND_FILE + 1][MAX_NR_ZONES];
 	/* the multi-gen LRU sizes, eventually consistent */
 	long nr_pages[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
 	/* the exponential moving average of refaulted */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 96abf4a52382..9dc665dc6ba9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3725,21 +3725,25 @@ static bool inc_min_seq(struct lruvec *lruvec, int type, bool can_swap)
 
 	/* prevent cold/hot inversion if force_scan is true */
 	for (zone = 0; zone < MAX_NR_ZONES; zone++) {
-		struct list_head *head = &lrugen->folios[old_gen][type][zone];
+		int list_num = type ? 2 : 1;
+		struct list_head *head;
 
-		while (!list_empty(head)) {
-			struct folio *folio = lru_to_folio(head);
+		for (int i = list_num - 1; i >= 0; i--) {
+			head = &lrugen->folios[old_gen][type + i][zone];
+			while (!list_empty(head)) {
+				struct folio *folio = lru_to_folio(head);
 
-			VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
-			VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
-			VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
-			VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
+				VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
+				VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
+				VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
+				VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
 
-			new_gen = folio_inc_gen(lruvec, folio, false);
-			list_move_tail(&folio->lru, &lrugen->folios[new_gen][type][zone]);
+				new_gen = folio_inc_gen(lruvec, folio, false);
+				list_move_tail(&folio->lru, &lrugen->folios[new_gen][type + i][zone]);
 
-			if (!--remaining)
-				return false;
+				if (!--remaining)
+					return false;
+			}
 		}
 	}
 done:
@@ -4291,6 +4295,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 	int refs = folio_lru_refs(folio);
 	int tier = lru_tier_from_refs(refs);
 	struct lru_gen_folio *lrugen = &lruvec->lrugen;
+	int lazyfree = type ? folio_test_anon(folio) : 0;
 
 	VM_WARN_ON_ONCE_FOLIO(gen >= MAX_NR_GENS, folio);
 
@@ -4306,7 +4311,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 
 	/* promoted */
 	if (gen != lru_gen_from_seq(lrugen->min_seq[type])) {
-		list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
+		list_move(&folio->lru, &lrugen->folios[gen][type + lazyfree][zone]);
 		return true;
 	}
 
@@ -4315,7 +4320,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 		int hist = lru_hist_from_seq(lrugen->min_seq[type]);
 
 		gen = folio_inc_gen(lruvec, folio, false);
-		list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
+		list_move_tail(&folio->lru, &lrugen->folios[gen][type + lazyfree][zone]);
 
 		WRITE_ONCE(lrugen->protected[hist][type][tier - 1],
 			   lrugen->protected[hist][type][tier - 1] + delta);
@@ -4325,7 +4330,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 	/* ineligible */
 	if (!folio_test_lru(folio) || zone > sc->reclaim_idx) {
 		gen = folio_inc_gen(lruvec, folio, false);
-		list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]);
+		list_move_tail(&folio->lru, &lrugen->folios[gen][type + lazyfree][zone]);
 		return true;
 	}
 
@@ -4333,7 +4338,7 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c
 	if (folio_test_locked(folio) || folio_test_writeback(folio) ||
 	    (type == LRU_GEN_FILE && folio_test_dirty(folio))) {
 		gen = folio_inc_gen(lruvec, folio, true);
-		list_move(&folio->lru, &lrugen->folios[gen][type][zone]);
+		list_move(&folio->lru, &lrugen->folios[gen][type + lazyfree][zone]);
 		return true;
 	}
 
@@ -4377,7 +4382,7 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca
 static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
 		       int type, int tier, struct list_head *list)
 {
-	int i;
+	int i, j;
 	int gen;
 	enum vm_event_item item;
 	int sorted = 0;
@@ -4399,33 +4404,38 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
 		LIST_HEAD(moved);
 		int skipped_zone = 0;
 		int zone = (sc->reclaim_idx + i) % MAX_NR_ZONES;
-		struct list_head *head = &lrugen->folios[gen][type][zone];
-
-		while (!list_empty(head)) {
-			struct folio *folio = lru_to_folio(head);
-			int delta = folio_nr_pages(folio);
-
-			VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
-			VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
-			VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
-			VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
-
-			scanned += delta;
+		int list_num = type ? 2 : 1;
+		struct list_head *head;
+
+		for (j = list_num - 1; j >= 0; j--) {
+			head = &lrugen->folios[gen][type + j][zone];
+			while (!list_empty(head)) {
+				struct folio *folio = lru_to_folio(head);
+				int delta = folio_nr_pages(folio);
+
+				VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
+				VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
+				VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
+				VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
+
+				scanned += delta;
+
+				if (sort_folio(lruvec, folio, sc, tier))
+					sorted += delta;
+				else if (isolate_folio(lruvec, folio, sc)) {
+					list_add(&folio->lru, list);
+					isolated += delta;
+				} else {
+					list_move(&folio->lru, &moved);
+					skipped_zone += delta;
+				}
 
-			if (sort_folio(lruvec, folio, sc, tier))
-				sorted += delta;
-			else if (isolate_folio(lruvec, folio, sc)) {
-				list_add(&folio->lru, list);
-				isolated += delta;
-			} else {
-				list_move(&folio->lru, &moved);
-				skipped_zone += delta;
+				if (!--remaining || max(isolated, skipped_zone) >= MIN_LRU_BATCH)
+					goto isolate_done;
 			}
-
-			if (!--remaining || max(isolated, skipped_zone) >= MIN_LRU_BATCH)
-				break;
 		}
 
+isolate_done:
 		if (skipped_zone) {
 			list_splice(&moved, head);
 			__count_zid_vm_events(PGSCAN_SKIP, zone, skipped_zone);
@@ -5586,8 +5596,15 @@ void lru_gen_init_lruvec(struct lruvec *lruvec)
 	for (i = 0; i <= MIN_NR_GENS + 1; i++)
 		lrugen->timestamps[i] = jiffies;
 
-	for_each_gen_type_zone(gen, type, zone)
+	for_each_gen_type_zone(gen, type, zone) {
 		INIT_LIST_HEAD(&lrugen->folios[gen][type][zone]);
+		/*
+		 * lazyfree anon folios have a separate list while using
+		 * file as type
+		 */
+		if (type)
+			INIT_LIST_HEAD(&lrugen->folios[gen][type + 1][zone]);
+	}
 
 	if (mm_state)
 		mm_state->seq = MIN_NR_GENS;
-- 
2.39.3 (Apple Git-146)