+ mm-huge_memory-consolidate-irq-and-locking-for-folio-split.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/huge_memory: consolidate irq and locking for folio split
has been added to the -mm mm-new branch.  Its filename is
     mm-huge_memory-consolidate-irq-and-locking-for-folio-split.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-consolidate-irq-and-locking-for-folio-split.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.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Kairui Song <kasong@tencent.com>
Subject: mm/huge_memory: consolidate irq and locking for folio split
Date: Tue, 15 Sep 2026 01:14:47 +0800

Let each split helper handle its own locking instead of relying on the
caller, so both helpers manage their own irq and locking state.  This lets
__folio_split() drop its local irq handling and fail label, preparing for
further cleanup.

The file path now uses xas_lock_irq() instead of local_irq_disable() with
xas_lock().  The two are equivalent on non-RT, and TRANSPARENT_HUGEPAGE
cannot be enabled on RT anyway.  This conversion also buys consistency:
every other place in mm/ that freezes a folio while it is still reachable
through the page cache already takes the lock this way.  This was actually
the last plain xas_lock() on mapping->i_pages left in mm.  If we are going
to support RT, spinning on frozen folio refs could be a problem, but it
already exists in many places and should be fixed generically.

The anon helper keeps a single local_irq_disable() as before, because it
has to cover several plain spinlocks at once.

The dropped xas_reset() was a no-op as the xa_state is not walked before
the xas_load() under the lock.

Link: https://lore.kernel.org/20260915-swap-thp-cleanup-v5-6-39878b37dfb0@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
---

 mm/huge_memory.c |   58 ++++++++++++++++++++-------------------------
 1 file changed, 27 insertions(+), 31 deletions(-)

--- a/mm/huge_memory.c~mm-huge_memory-consolidate-irq-and-locking-for-folio-split
+++ a/mm/huge_memory.c
@@ -4021,8 +4021,12 @@ static int __folio_freeze_split_anon(str
 	struct lruvec *lruvec;
 	int ret = 0;
 
-	if (!folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1))
+	local_irq_disable();
+
+	if (!folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1)) {
+		local_irq_enable();
 		return -EAGAIN;
+	}
 
 	/* Take off the deferred split queue while frozen and memcg set */
 	folio_unqueue_deferred_split(folio);
@@ -4070,6 +4074,7 @@ static int __folio_freeze_split_anon(str
 		lruvec_unlock(lruvec);
 	if (ci)
 		swap_cluster_unlock(ci);
+	local_irq_enable();
 
 	return ret;
 }
@@ -4088,8 +4093,21 @@ static int __folio_freeze_split_file(str
 	/* Currently device private folios can only back anonymous memory. */
 	VM_WARN_ON_ONCE_FOLIO(folio_is_device_private(folio), folio);
 
-	if (!folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1))
-		return -EAGAIN;
+	xas_lock_irq(xas);
+
+	/*
+	 * Check if the folio is present in page cache.
+	 * We assume all tail are present too, if folio is there.
+	 */
+	if (xas_load(xas) != folio) {
+		ret = -EAGAIN;
+		goto fail;
+	}
+
+	if (!folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1)) {
+		ret = -EAGAIN;
+		goto fail;
+	}
 
 	if (folio_test_pmd_mappable(folio) &&
 	    new_order < HPAGE_PMD_ORDER) {
@@ -4161,6 +4179,8 @@ static int __folio_freeze_split_file(str
 	if (do_lru)
 		lruvec_unlock(lruvec);
 
+fail:
+	xas_unlock_irq(xas);
 	return ret;
 }
 
@@ -4300,32 +4320,13 @@ static int __folio_split(struct folio *f
 
 	unmap_folio(folio);
 
-	/* block interrupt reentry in xa_lock and spinlock */
-	local_irq_disable();
-	if (is_anon) {
+	if (is_anon)
 		ret = __folio_freeze_split_anon(folio, new_order, split_at,
 						true, list, split_type);
-	} else {
-		/*
-		 * Check if the folio is present in page cache.
-		 * We assume all tail are present too, if folio is there.
-		 */
-		xas_lock(&xas);
-		xas_reset(&xas);
-		if (xas_load(&xas) != folio) {
-			ret = -EAGAIN;
-			goto fail;
-		}
+	else
 		ret = __folio_freeze_split_file(folio, new_order, split_at, &xas, mapping,
 						true, list, split_type, end,
 						&nr_shmem_dropped);
-	}
-
-fail:
-	if (mapping)
-		xas_unlock(&xas);
-
-	local_irq_enable();
 
 	if (nr_shmem_dropped)
 		shmem_uncharge(mapping->host, nr_shmem_dropped);
@@ -4409,8 +4410,6 @@ out_no_memcg:
  */
 int folio_split_unmapped(struct folio *folio, unsigned int new_order)
 {
-	int ret = 0;
-
 	VM_WARN_ON_ONCE_FOLIO(folio_mapped(folio), folio);
 	VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
 	VM_WARN_ON_ONCE_FOLIO(!folio_test_large(folio), folio);
@@ -4419,11 +4418,8 @@ int folio_split_unmapped(struct folio *f
 	if (folio_expected_ref_count(folio) != folio_ref_count(folio) - 1)
 		return -EAGAIN;
 
-	local_irq_disable();
-	ret = __folio_freeze_split_anon(folio, new_order, &folio->page,
-					false, NULL, SPLIT_TYPE_UNIFORM);
-	local_irq_enable();
-	return ret;
+	return __folio_freeze_split_anon(folio, new_order, &folio->page,
+					 false, NULL, SPLIT_TYPE_UNIFORM);
 }
 
 /*
_

Patches currently in -mm which might be from kasong@tencent.com are

mm-memcontrol-move-the-lru_zone_size-sanity-check-to-the-reader-side.patch
mm-mglru-introduce-helpers-for-manipulating-gen-and-refs-flags.patch
mm-migrate-copy-all-referenced-state-via-folio_migrate_lru_refs.patch
mm-mglru-move-max_seq-read-into-walk_update_folio.patch
mm-mglru-use-explicit-tier-range-in-read_ctrl_pos.patch
mm-mglru-fix-potential-generation-folio-number-leak.patch
mm-swap-fix-off-by-one-in-swap-cache-replace-sanity-check.patch
mm-huge_memory-fix-rejection-of-swap-cache-folios-with-a-mapping.patch
mm-huge_memory-invert-folio_ref_freeze-check-to-reduce-indentation.patch
mm-huge_memory-split-the-routine-for-splitting-anon-and-file-folio.patch
mm-huge_memory-rename-__split_unmapped_folio-to-__split_frozen_folio.patch
mm-huge_memory-consolidate-irq-and-locking-for-folio-split.patch
mm-huge_memory-move-eof-trimming-into-the-file-split-helper.patch
mm-huge_memory-move-unmap-and-remap-into-the-split-helpers.patch
mm-huge_memory-rename-remap_page-to-remap_anon_folio.patch
mm-huge_memory-move-the-racy-refcount-check-into-unmap_folio.patch
mm-huge_memory-move-filemap-management-into-the-file-split-helper.patch
mm-huge_memory-move-anon_vma-handling-into-the-anon-split-helper.patch
mm-huge_memory-move-memcg-switch-into-the-file-split-helper.patch
mm-huge_memory-drop-the-unused-do_lru-argument-of-the-file-split-helper.patch
mm-huge_memory-clean-up-after-split-folio-freeing-in-__folio_split.patch
mm-huge_memory-count-only-swap-cache-refs-in-anon-folio-split.patch
mm-huge_memory-drop-the-redundant-mapping-argument-of-__split_frozen_folio.patch