+ mm-optimize-lru_note_cost-by-adding-lru_note_cost_unlock_irq.patch added to mm-new branch

+ mm-optimize-lru_note_cost-by-adding-lru_note_cost_unlock_irq.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm: optimize lru_note_cost() by adding lru_note_cost_unlock_irq()
has been added to the -mm mm-new branch.  Its filename is
     mm-optimize-lru_note_cost-by-adding-lru_note_cost_unlock_irq.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-optimize-lru_note_cost-by-adding-lru_note_cost_unlock_irq.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
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fixup patches in mm-new.

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------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: mm: optimize lru_note_cost() by adding lru_note_cost_unlock_irq()
Date: Sun, 13 Jul 2025 12:57:18 -0700 (PDT)

Dropping a lock, just to demand it again for an afterthought, cannot be
good if contended: convert lru_note_cost() to lru_note_cost_unlock_irq().

Link: https://lkml.kernel.org/r/21100102-51b6-79d5-03db-1bb7f97fa94c@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Tested-by: Roman Gushchin <roman.gushchin@linux.dev>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: David Hildenbrand <david@redhat.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/swap.h |    5 +++--
 mm/swap.c            |   26 +++++++++++++++++++-------
 mm/vmscan.c          |    8 +++-----
 3 files changed, 25 insertions(+), 14 deletions(-)

--- a/include/linux/swap.h~mm-optimize-lru_note_cost-by-adding-lru_note_cost_unlock_irq
+++ a/include/linux/swap.h
@@ -376,8 +376,9 @@ extern unsigned long totalreserve_pages;
 
 
 /* linux/mm/swap.c */
-void lru_note_cost(struct lruvec *lruvec, bool file,
-		   unsigned int nr_io, unsigned int nr_rotated);
+void lru_note_cost_unlock_irq(struct lruvec *lruvec, bool file,
+		unsigned int nr_io, unsigned int nr_rotated)
+		__releases(lruvec->lru_lock);
 void lru_note_cost_refault(struct folio *);
 void folio_add_lru(struct folio *);
 void folio_add_lru_vma(struct folio *, struct vm_area_struct *);
--- a/mm/swap.c~mm-optimize-lru_note_cost-by-adding-lru_note_cost_unlock_irq
+++ a/mm/swap.c
@@ -237,8 +237,9 @@ void folio_rotate_reclaimable(struct fol
 	folio_batch_add_and_move(folio, lru_move_tail, true);
 }
 
-void lru_note_cost(struct lruvec *lruvec, bool file,
-		   unsigned int nr_io, unsigned int nr_rotated)
+void lru_note_cost_unlock_irq(struct lruvec *lruvec, bool file,
+		unsigned int nr_io, unsigned int nr_rotated)
+		__releases(lruvec->lru_lock)
 {
 	unsigned long cost;
 
@@ -250,8 +251,12 @@ void lru_note_cost(struct lruvec *lruvec
 	 * different between them, adjust scan balance for CPU work.
 	 */
 	cost = nr_io * SWAP_CLUSTER_MAX + nr_rotated;
+	if (!cost) {
+		spin_unlock_irq(&lruvec->lru_lock);
+		return;
+	}
 
-	do {
+	for (;;) {
 		unsigned long lrusize;
 
 		/*
@@ -261,7 +266,6 @@ void lru_note_cost(struct lruvec *lruvec
 		 *    rcu lock, so would be safe even if the page was on the LRU
 		 *    and could move simultaneously to a new lruvec).
 		 */
-		spin_lock_irq(&lruvec->lru_lock);
 		/* Record cost event */
 		if (file)
 			lruvec->file_cost += cost;
@@ -285,14 +289,22 @@ void lru_note_cost(struct lruvec *lruvec
 			lruvec->file_cost /= 2;
 			lruvec->anon_cost /= 2;
 		}
+
 		spin_unlock_irq(&lruvec->lru_lock);
-	} while ((lruvec = parent_lruvec(lruvec)));
+		lruvec = parent_lruvec(lruvec);
+		if (!lruvec)
+			break;
+		spin_lock_irq(&lruvec->lru_lock);
+	}
 }
 
 void lru_note_cost_refault(struct folio *folio)
 {
-	lru_note_cost(folio_lruvec(folio), folio_is_file_lru(folio),
-		      folio_nr_pages(folio), 0);
+	struct lruvec *lruvec;
+
+	lruvec = folio_lruvec_lock_irq(folio);
+	lru_note_cost_unlock_irq(lruvec, folio_is_file_lru(folio),
+				folio_nr_pages(folio), 0);
 }
 
 static void lru_activate(struct lruvec *lruvec, struct folio *folio)
--- a/mm/vmscan.c~mm-optimize-lru_note_cost-by-adding-lru_note_cost_unlock_irq
+++ a/mm/vmscan.c
@@ -2061,9 +2061,9 @@ static unsigned long shrink_inactive_lis
 		__count_vm_events(item, nr_reclaimed);
 	count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
 	__count_vm_events(PGSTEAL_ANON + file, nr_reclaimed);
-	spin_unlock_irq(&lruvec->lru_lock);
 
-	lru_note_cost(lruvec, file, stat.nr_pageout, nr_scanned - nr_reclaimed);
+	lru_note_cost_unlock_irq(lruvec, file, stat.nr_pageout,
+					nr_scanned - nr_reclaimed);
 
 	/*
 	 * If dirty folios are scanned that are not queued for IO, it
@@ -2209,10 +2209,8 @@ static void shrink_active_list(unsigned
 	count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, nr_deactivate);
 
 	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
-	spin_unlock_irq(&lruvec->lru_lock);
 
-	if (nr_rotated)
-		lru_note_cost(lruvec, file, 0, nr_rotated);
+	lru_note_cost_unlock_irq(lruvec, file, 0, nr_rotated);
 	trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
 			nr_deactivate, nr_rotated, sc->priority, file);
 }
_

Patches currently in -mm which might be from hughd@google.com are

mm-optimize-lru_note_cost-by-adding-lru_note_cost_unlock_irq.patch