+ mm-huge_memory-use-folio_expected_ref_count-to-calculate-ref_count.patch added to mm-unstable branch

+ mm-huge_memory-use-folio_expected_ref_count-to-calculate-ref_count.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/huge_memory: use folio_expected_ref_count() to calculate ref_count
has been added to the -mm mm-unstable branch.  Its filename is
     mm-huge_memory-use-folio_expected_ref_count-to-calculate-ref_count.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-use-folio_expected_ref_count-to-calculate-ref_count.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Zi Yan <ziy@nvidia.com>
Subject: mm/huge_memory: use folio_expected_ref_count() to calculate ref_count
Date: Mon, 14 Jul 2025 13:18:23 -0400

Patch series "__folio_split() clean up." v3.

Based on the prior discussion[1], this patch improves
__split_unmapped_folio() by making it reusable for splitting unmapped
folios.  This helps avoid the need for a new boolean unmapped parameter to
guard mapping-related code.

An additional benefit is that __split_unmapped_folio() could be called on
after-split folios by __folio_split().  It can enable new split methods. 
For example, at deferred split time, unmapped subpages can scatter
arbitrarily within a large folio, neither uniform nor non-uniform split
can maximize after-split folio orders for mapped subpages.  The hope is
that by calling __split_unmapped_folio() multiple times, a better split
result can be achieved.


This patch (of 2):

Instead of open coding the ref_count calculation, use
folio_expected_ref_count().

Link: https://lkml.kernel.org/r/20250714171823.3626213-3-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: Balbir Singh <balbirs@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kirill A. Shutemov <k.shutemov@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

--- a/mm/huge_memory.c~mm-huge_memory-use-folio_expected_ref_count-to-calculate-ref_count
+++ a/mm/huge_memory.c
@@ -3724,6 +3724,7 @@ static int __folio_split(struct folio *f
 	if (folio_ref_freeze(folio, 1 + extra_pins)) {
 		struct address_space *swap_cache = NULL;
 		struct lruvec *lruvec;
+		int expected_refs;
 
 		if (folio_order(folio) > 1 &&
 		    !list_empty(&folio->_deferred_list)) {
@@ -3794,11 +3795,8 @@ static int __folio_split(struct folio *f
 		     new_folio = next) {
 			next = folio_next(new_folio);
 
-			folio_ref_unfreeze(
-				new_folio,
-				1 + ((mapping || swap_cache) ?
-					     folio_nr_pages(new_folio) :
-					     0));
+			expected_refs = folio_expected_ref_count(new_folio) + 1;
+			folio_ref_unfreeze(new_folio, expected_refs);
 
 			lru_add_split_folio(folio, new_folio, lruvec, list);
 
@@ -3828,8 +3826,8 @@ static int __folio_split(struct folio *f
 		 * Otherwise, a parallel folio_try_get() can grab origin_folio
 		 * and its caller can see stale page cache entries.
 		 */
-		folio_ref_unfreeze(folio, 1 +
-			((mapping || swap_cache) ? folio_nr_pages(folio) : 0));
+		expected_refs = folio_expected_ref_count(folio) + 1;
+		folio_ref_unfreeze(folio, expected_refs);
 
 		unlock_page_lruvec(lruvec);
 
_

Patches currently in -mm which might be from ziy@nvidia.com are

selftests-mm-fix-split_huge_page_test-for-folio_split-tests.patch
mm-huge_memory-move-unrelated-code-out-of-__split_unmapped_folio.patch
mm-huge_memory-use-folio_expected_ref_count-to-calculate-ref_count.patch