Commit a8682d50 authored Dec 23, 2025 by David Hildenbrand (Red Hat) Committed by Andrew Morton Jan 20, 2026

mm/rmap: fix two comments related to huge_pmd_unshare()

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: 59d9094d ("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>

parent 3937027c

mm/rmap.c

+4 −16

Original line number	Diff line number	Diff line
		@@ -2016,14 +2016,8 @@ static bool try_to_unmap_one(struct folio folio, struct vm_area_struct vma,
		flush_tlb_range(vma,
		range.start, 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.
		*/
		goto walk_done;
		}
		@@ -2416,14 +2410,8 @@ static bool try_to_migrate_one(struct folio folio, struct vm_area_struct vma,
		range.start, 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;