mm-mglru-preserve-inactive-placement-when-enabling-mglru.patch removed from -mm tree

The quilt patch titled
Subject: mm/mglru: preserve inactive placement when enabling MGLRU
has been removed from the -mm tree. Its filename was
mm-mglru-preserve-inactive-placement-when-enabling-mglru.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Ridong Chen <[email protected]>
Subject: mm/mglru: preserve inactive placement when enabling MGLRU
Date: Fri, 21 Aug 2026 10:16:06 +0800

When the LRU is switched to MGLRU (echo y > /sys/kernel/mm/lru_gen/ enabled), fill_evictable() re-inserts every folio via lru_gen_add_folio(..., false). With reclaiming hardcoded to false, an inactive anonymous folio (no PG_active, not in the swapcache) takes the "gen = MIN_NR_GENS" branch in lru_gen_folio_seq() and is seeded at seq = max_seq - 1, which lru_gen_is_active() treats as active. Its inactive placement is lost and NR_INACTIVE_ANON is folded into NR_ACTIVE_ANON.

Pass reclaiming=!active so a folio from an inactive list is seeded into an older generation. Folios from the active list carry PG_active and hit the first branch either way, so they are unchanged.

Reclaiming also selects the insertion end in lru_gen_add_folio():
list_add_tail() for inactive folios, list_add() for active ones. Both the legacy LRU and a MGLRU generation keep the hottest folios at the head and the coldest at the tail, and reclaim takes from the tail. To preserve that order the folio must be taken from the end matching the insertion end, so take inactive folios from the head and active folios from the tail; otherwise hot/cold would be reversed within the generation.

Tested on x86_64, next-20260812, 2G VM + 1G swap, ~1.5G anon pushed onto the inactive list before enabling MGLRU:

Active(anon) Inactive(anon)

  before switch (legacy)        2952         1548792   kB
  after `echo y`, unpatched  1552052               0   kB
  after `echo y`, patched      15144         1536636   kB

Inactive file folios stay inactive either way (NR_INACTIVE_FILE is preserved).

---

 mm/vmscan.c |   18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

@@ -5307,7 +5307,17 @@ static bool fill_evictable(struct lruvec
 
 		while (!list_empty(head)) {
 			bool success;
-			struct folio *folio = lru_to_folio(head);
+			struct folio *folio;
+
+			/*
+			 * lru_gen_add_folio() uses list_add_tail() rather
+			 * than list_add() when reclaiming is true.  Match
+			 * its ordering to avoid cold/hot inversion.
+			 */
+			if (active)
+				folio = lru_to_folio(head);
+			else
+				folio = list_first_entry(head, struct folio, lru);
 
 			VM_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
 			VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio) != active, folio);

@@ -5315,7 +5325,11 @@ static bool fill_evictable(struct lruvec
 			VM_WARN_ON_ONCE_FOLIO(folio_lru_gen(folio) != -1, folio);
 
 			lruvec_del_folio(lruvec, folio);
-			success = lru_gen_add_folio(lruvec, folio, false);
+			/*
+			 * Borrow reclaiming=true to place inactive folios in
+			 * the older gens.
+			 */
+			success = lru_gen_add_folio(lruvec, folio, !active);
 			VM_WARN_ON_ONCE(!success);
 
 			if (!--remaining)

_

Patches currently in -mm which might be from [email protected] are

mm-page_counter-avoid-integer-overflow-in-effective_protection.patch mm-mglru-fix-ineffective-memory-protection-for-non-kswapd-reclaim.patch mm-vmscan-put-rotation-missed-folios-at-the-lru-tail.patch