[PATCH 5.15.y 5/6] mm/rmap: fix two comments related to huge_pmd_unshare()

David Hildenbrand (Arm)
2026-02-18T11:01:56Z

From: "David Hildenbrand (Red Hat)" <david@kernel.org>

PMD page table unsharing no longer touches the refcount of a PMD page
table. Also, it is not about dropping the refcount of a "PMD page" but
the "PMD page table".

Let's just simplify by saying that the PMD page table was unmapped,
consequently also unmapping the folio that was mapped into this page.

This code should be deduplicated in the future.

Link: https://lkml.kernel.org/r/20251223214037.580860-4-david@kernel.org
Fixes: 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count")
Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Rik van Riel <riel@surriel.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Cc: Liu Shixin <liushixin2@huawei.com>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: "Uschakow, Stanislav" <suschako@amazon.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit a8682d500f691b6dfaa16ae1502d990aeb86e8be)
[ David: We don't have 40549ba8f8e0 ("hugetlb: use new vma_lock
for pmd sharing synchronization") so there are some contextual
differences. ]
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
mm/rmap.c | 18 ++++--------------
1 file changed, 4 insertions(+), 14 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index cb133bd49e02..5093d53f196e 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1489,13 +1489,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
range.end);

/*
- * The ref count of the PMD page was dropped
- * which is part of the way map counting
- * is done for shared PMDs. Return 'true'
- * here. When there is no other sharing,
- * huge_pmd_unshare returns false and we will
- * unmap the actual page and drop map count
- * to zero.
+ * The PMD table was unmapped,
+ * consequently unmapping the folio.
*/
page_vma_mapped_walk_done(&pvmw);
break;
@@ -1808,13 +1803,8 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
range.end);

/*
- * The ref count of the PMD page was dropped
- * which is part of the way map counting
- * is done for shared PMDs. Return 'true'
- * here. When there is no other sharing,
- * huge_pmd_unshare returns false and we will
- * unmap the actual page and drop map count
- * to zero.
+ * The PMD table was unmapped,
+ * consequently unmapping the folio.
*/
page_vma_mapped_walk_done(&pvmw);
break;
--
2.43.0