+ mm-huge_memory-update-folio-stat-after-successful-split.patch added to mm-new branch

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

The patch titled
     Subject: mm/huge_memory: update folio stat after successful split
has been added to the -mm mm-new branch.  Its filename is
     mm-huge_memory-update-folio-stat-after-successful-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-update-folio-stat-after-successful-split.patch

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

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------------------------------------------------------
From: Wei Yang <richard.weiyang@gmail.com>
Subject: mm/huge_memory: update folio stat after successful split
Date: Tue, 14 Oct 2025 13:46:03 +0000

When a folio is successfully split, its statistics must be updated.

The current implementation complicates this process:

  * It iterates over the resulting new folios.
  * It uses a flag (@stop_split) to conditionally skip updating the stat
    for the folio at @split_at during the loop.
  * It then attempts to update the skipped stat on a subsequent failure
    path.

This logic is unnecessarily hard to follow.

This commit refactors the code to update the folio statistics only after a
successful split.  This makes the logic much cleaner and sets the stage
for further simplification of the stat-handling code.

Link: https://lkml.kernel.org/r/20251014134606.22543-3-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
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 |   44 +++++++++++---------------------------------
 1 file changed, 11 insertions(+), 33 deletions(-)

--- a/mm/huge_memory.c~mm-huge_memory-update-folio-stat-after-successful-split
+++ a/mm/huge_memory.c
@@ -3530,13 +3530,8 @@ static int __split_unmapped_folio(struct
 	bool is_anon = folio_test_anon(folio);
 	int order = folio_order(folio);
 	int start_order = uniform_split ? new_order : order - 1;
-	bool stop_split = false;
 	struct folio *next;
 	int split_order;
-	int ret = 0;
-
-	if (is_anon)
-		mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
 
 	folio_clear_has_hwpoisoned(folio);
 
@@ -3545,7 +3540,7 @@ static int __split_unmapped_folio(struct
 	 * folio is split to new_order directly.
 	 */
 	for (split_order = start_order;
-	     split_order >= new_order && !stop_split;
+	     split_order >= new_order;
 	     split_order--) {
 		struct folio *end_folio = folio_next(folio);
 		int old_order = folio_order(folio);
@@ -3568,49 +3563,32 @@ static int __split_unmapped_folio(struct
 			else {
 				xas_set_order(xas, folio->index, split_order);
 				xas_try_split(xas, folio, old_order);
-				if (xas_error(xas)) {
-					ret = xas_error(xas);
-					stop_split = true;
-				}
+				if (xas_error(xas))
+					return xas_error(xas);
 			}
 		}
 
-		if (!stop_split) {
-			folio_split_memcg_refs(folio, old_order, split_order);
-			split_page_owner(&folio->page, old_order, split_order);
-			pgalloc_tag_split(folio, old_order, split_order);
-
-			__split_folio_to_order(folio, old_order, split_order);
-		}
+		folio_split_memcg_refs(folio, old_order, split_order);
+		split_page_owner(&folio->page, old_order, split_order);
+		pgalloc_tag_split(folio, old_order, split_order);
+		__split_folio_to_order(folio, old_order, split_order);
 
+		if (is_anon)
+			mod_mthp_stat(old_order, MTHP_STAT_NR_ANON, -1);
 		/*
 		 * Iterate through after-split folios and update folio stats.
-		 * But in buddy allocator like split, the folio
-		 * containing the specified page is skipped until its order
-		 * is new_order, since the folio will be worked on in next
-		 * iteration.
 		 */
 		for (new_folio = folio; new_folio != end_folio; new_folio = next) {
 			next = folio_next(new_folio);
-			/*
-			 * for buddy allocator like split, new_folio containing
-			 * @split_at page could be split again, thus do not
-			 * change stats yet. Wait until new_folio's order is
-			 * @new_order or stop_split is set to true by the above
-			 * xas_split() failure.
-			 */
-			if (new_folio == page_folio(split_at)) {
+			if (new_folio == page_folio(split_at))
 				folio = new_folio;
-				if (split_order != new_order && !stop_split)
-					continue;
-			}
 			if (is_anon)
 				mod_mthp_stat(folio_order(new_folio),
 					      MTHP_STAT_NR_ANON, 1);
 		}
 	}
 
-	return ret;
+	return 0;
 }
 
 bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
_

Patches currently in -mm which might be from richard.weiyang@gmail.com are

mm-compaction-check-the-range-to-pageblock_pfn_to_page-is-within-the-zone-first.patch
mm-compaction-fix-the-range-to-pageblock_pfn_to_page.patch
mm-huge_memory-add-pmd-folio-to-ds_queue-in-do_huge_zero_wp_pmd.patch
mm-khugepaged-unify-pmd-folio-installation-with-map_anon_folio_pmd.patch
mm-huge_memory-only-get-folio_order-once-during-__folio_split.patch
mm-huge_memory-cache-folio-attribute-in-__split_unmapped_folio.patch
mm-huge_memory-update-folio-stat-after-successful-split.patch
mm-huge_memory-optimize-and-simplify-folio-stat-update-after-split.patch
mm-huge_memory-optimize-old_order-derivation-during-folio-splitting.patch
mm-huge_memory-remove-redundant-split_order-=-new_order-check-in-uniform_split.patch