+ mm-revert-mm-gup-clear-the-lru-flag-of-a-page-before-adding-to-lru-batch.patch added to mm-new branch

+ mm-revert-mm-gup-clear-the-lru-flag-of-a-page-before-adding-to-lru-batch.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm: Revert "mm/gup: clear the LRU flag of a page before adding to LRU batch"
has been added to the -mm mm-new branch.  Its filename is
     mm-revert-mm-gup-clear-the-lru-flag-of-a-page-before-adding-to-lru-batch.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-revert-mm-gup-clear-the-lru-flag-of-a-page-before-adding-to-lru-batch.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
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: mm: Revert "mm/gup: clear the LRU flag of a page before adding to LRU batch"
Date: Sun, 31 Aug 2025 02:11:33 -0700 (PDT)

This reverts commit 33dfe9204f29b415bbc0abb1a50642d1ba94f5e9: now that
collect_longterm_unpinnable_folios() is checking ref_count instead of lru,
and mlock/munlock do not participate in the revised LRU flag clearing,
those changes are misleading, and enlarge the window during which
mlock/munlock may miss an mlock_count update.

It is possible (I'd hesitate to claim probable) that the greater
likelihood of missed mlock_count updates would explain the "Realtime
threads delayed due to kcompactd0" observed on 6.12 in the Link below.  If
that is the case, this reversion will help; but a complete solution needs
also a further patch, beyond the scope of this series.

Included some 80-column cleanup around folio_batch_add_and_move().

The role of folio_test_clear_lru() (before taking per-memcg lru_lock) is
questionable since 6.13 removed mem_cgroup_move_account() etc; but perhaps
there are still some races which need it - not examined here.

Link: https://lore.kernel.org/linux-mm/DU0PR01MB10385345F7153F334100981888259A@DU0PR01MB10385.eurprd01.prod.exchangelabs.com/
Link: https://lkml.kernel.org/r/0215a42b-99cd-612a-95f7-56f8251d99ef@google.com
Fixes: 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch")
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Keir Fraser <keirf@google.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Li Zhe <lizhe.67@bytedance.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shivank Garg <shivankg@amd.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Xu <weixugc@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: yangge <yangge1116@126.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/swap.c |   50 ++++++++++++++++++++++++++------------------------
 1 file changed, 26 insertions(+), 24 deletions(-)

--- a/mm/swap.c~mm-revert-mm-gup-clear-the-lru-flag-of-a-page-before-adding-to-lru-batch
+++ a/mm/swap.c
@@ -164,6 +164,10 @@ static void folio_batch_move_lru(struct
 	for (i = 0; i < folio_batch_count(fbatch); i++) {
 		struct folio *folio = fbatch->folios[i];
 
+		/* block memcg migration while the folio moves between lru */
+		if (move_fn != lru_add && !folio_test_clear_lru(folio))
+			continue;
+
 		folio_lruvec_relock_irqsave(folio, &lruvec, &flags);
 		move_fn(lruvec, folio);
 
@@ -176,14 +180,10 @@ static void folio_batch_move_lru(struct
 }
 
 static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch,
-		struct folio *folio, move_fn_t move_fn,
-		bool on_lru, bool disable_irq)
+		struct folio *folio, move_fn_t move_fn, bool disable_irq)
 {
 	unsigned long flags;
 
-	if (on_lru && !folio_test_clear_lru(folio))
-		return;
-
 	folio_get(folio);
 
 	if (disable_irq)
@@ -191,8 +191,8 @@ static void __folio_batch_add_and_move(s
 	else
 		local_lock(&cpu_fbatches.lock);
 
-	if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || folio_test_large(folio) ||
-	    lru_cache_disabled())
+	if (!folio_batch_add(this_cpu_ptr(fbatch), folio) ||
+			folio_test_large(folio) || lru_cache_disabled())
 		folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn);
 
 	if (disable_irq)
@@ -201,13 +201,13 @@ static void __folio_batch_add_and_move(s
 		local_unlock(&cpu_fbatches.lock);
 }
 
-#define folio_batch_add_and_move(folio, op, on_lru)						\
-	__folio_batch_add_and_move(								\
-		&cpu_fbatches.op,								\
-		folio,										\
-		op,										\
-		on_lru,										\
-		offsetof(struct cpu_fbatches, op) >= offsetof(struct cpu_fbatches, lock_irq)	\
+#define folio_batch_add_and_move(folio, op)		\
+	__folio_batch_add_and_move(			\
+		&cpu_fbatches.op,			\
+		folio,					\
+		op,					\
+		offsetof(struct cpu_fbatches, op) >=	\
+		offsetof(struct cpu_fbatches, lock_irq)	\
 	)
 
 static void lru_move_tail(struct lruvec *lruvec, struct folio *folio)
@@ -231,10 +231,10 @@ static void lru_move_tail(struct lruvec
 void folio_rotate_reclaimable(struct folio *folio)
 {
 	if (folio_test_locked(folio) || folio_test_dirty(folio) ||
-	    folio_test_unevictable(folio))
+	    folio_test_unevictable(folio) || !folio_test_lru(folio))
 		return;
 
-	folio_batch_add_and_move(folio, lru_move_tail, true);
+	folio_batch_add_and_move(folio, lru_move_tail);
 }
 
 void lru_note_cost_unlock_irq(struct lruvec *lruvec, bool file,
@@ -328,10 +328,11 @@ static void folio_activate_drain(int cpu
 
 void folio_activate(struct folio *folio)
 {
-	if (folio_test_active(folio) || folio_test_unevictable(folio))
+	if (folio_test_active(folio) || folio_test_unevictable(folio) ||
+	    !folio_test_lru(folio))
 		return;
 
-	folio_batch_add_and_move(folio, lru_activate, true);
+	folio_batch_add_and_move(folio, lru_activate);
 }
 
 #else
@@ -507,7 +508,7 @@ void folio_add_lru(struct folio *folio)
 	    lru_gen_in_fault() && !(current->flags & PF_MEMALLOC))
 		folio_set_active(folio);
 
-	folio_batch_add_and_move(folio, lru_add, false);
+	folio_batch_add_and_move(folio, lru_add);
 }
 EXPORT_SYMBOL(folio_add_lru);
 
@@ -685,13 +686,13 @@ void lru_add_drain_cpu(int cpu)
 void deactivate_file_folio(struct folio *folio)
 {
 	/* Deactivating an unevictable folio will not accelerate reclaim */
-	if (folio_test_unevictable(folio))
+	if (folio_test_unevictable(folio) || !folio_test_lru(folio))
 		return;
 
 	if (lru_gen_enabled() && lru_gen_clear_refs(folio))
 		return;
 
-	folio_batch_add_and_move(folio, lru_deactivate_file, true);
+	folio_batch_add_and_move(folio, lru_deactivate_file);
 }
 
 /*
@@ -704,13 +705,13 @@ void deactivate_file_folio(struct folio
  */
 void folio_deactivate(struct folio *folio)
 {
-	if (folio_test_unevictable(folio))
+	if (folio_test_unevictable(folio) || !folio_test_lru(folio))
 		return;
 
 	if (lru_gen_enabled() ? lru_gen_clear_refs(folio) : !folio_test_active(folio))
 		return;
 
-	folio_batch_add_and_move(folio, lru_deactivate, true);
+	folio_batch_add_and_move(folio, lru_deactivate);
 }
 
 /**
@@ -723,10 +724,11 @@ void folio_deactivate(struct folio *foli
 void folio_mark_lazyfree(struct folio *folio)
 {
 	if (!folio_test_anon(folio) || !folio_test_swapbacked(folio) ||
+	    !folio_test_lru(folio) ||
 	    folio_test_swapcache(folio) || folio_test_unevictable(folio))
 		return;
 
-	folio_batch_add_and_move(folio, lru_lazyfree, true);
+	folio_batch_add_and_move(folio, lru_lazyfree);
 }
 
 void lru_add_drain(void)
_

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

mm-fix-folio_expected_ref_count-when-pg_private_2.patch
mm-gup-check-ref_count-instead-of-lru-before-migration.patch
mm-gup-local-lru_add_drain-to-avoid-lru_add_drain_all.patch
mm-revert-mm-gup-clear-the-lru-flag-of-a-page-before-adding-to-lru-batch.patch
mm-revert-mm-vmscanc-fix-oom-on-swap-stress-test.patch
mm-folio_may_be_cached-unless-folio_test_large.patch
mm-lru_add_drain_all-do-local-lru_add_drain-first.patch