+ mm-huge_memory-fix-outdated-comment-about-freeing-subpages-in-__folio_split.patch added to mm-new branch

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

The patch titled
     Subject: mm/huge_memory: Fix outdated comment about freeing subpages in __folio_split
has been added to the -mm mm-new branch.  Its filename is
     mm-huge_memory-fix-outdated-comment-about-freeing-subpages-in-__folio_split.patch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     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-fix-outdated-comment-about-freeing-subpages-in-__folio_split.patch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: "Barry Song (Xiaomi)" <baohua@kernel.org>
Subject: mm/huge_memory: Fix outdated comment about freeing subpages in __folio_split
Date: Thu, 23 Apr 2026 11:49:17 +0800

The comment appears to be outdated.  First, add_to_swap() no longer exists
after Kairui's commit b487a2da3575 ("mm, swap: simplify folio swap
allocation").  Second, partially zapped folios are now always split before
folio_alloc_swap() to avoid extra I/O, following Ryan's commit
5ed890ce5147 ("mm: vmscan: avoid split during shrink_folio_list()").  Fix
this by making the description more generic.

Link: https://lore.kernel.org/20260423034917.8234-1-baohua@kernel.org
Signed-off-by: Barry Song (Xiaomi) <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Youngjun Park <youngjun.park@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/mm/huge_memory.c~mm-huge_memory-fix-outdated-comment-about-freeing-subpages-in-__folio_split
+++ a/mm/huge_memory.c
@@ -4190,11 +4190,10 @@ fail:
 
 		folio_unlock(new_folio);
 		/*
-		 * Subpages may be freed if there wasn't any mapping
-		 * like if add_to_swap() is running on a lru page that
-		 * had its mapping zapped. And freeing these pages
-		 * requires taking the lru_lock so we do the put_page
-		 * of the tail pages after the split is complete.
+		 * Subpages whose mapping has been zapped may be freed
+		 * earlier, but freeing them requires taking the
+		 * lru_lock, so we defer put_page() on tail pages until
+		 * after the split completes.
 		 */
 		free_folio_and_swap_cache(new_folio);
 	}
_

Patches currently in -mm which might be from baohua@kernel.org are

mm-huge_memory-fix-outdated-comment-about-freeing-subpages-in-__folio_split.patch