[PATCH] mm/huge_memory: Fix outdated comment about freeing subpages in __folio_split

[PATCH] mm/huge_memory: Fix outdated comment about freeing subpages in __folio_split

[Barry Song (Xiaomi)]

The comment appears to be outdated.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.

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.Howlett@oracle.com>
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: Barry Song (Xiaomi) <baohua@kernel.org>
---
 mm/huge_memory.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 970e077019b7..4586f3ccb133 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4190,11 +4190,10 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
 
 		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);
 	}
-- 
2.39.3 (Apple Git-146)