mm-page_owner-extract-skip_buddy_pages-helper-to-unify-buddy-page-skipping.patch removed from -mm tree

The quilt patch titled
Subject: mm/page_owner: extract skip_buddy_pages() helper to unify buddy page skipping
has been removed from the -mm tree. Its filename was
mm-page_owner-extract-skip_buddy_pages-helper-to-unify-buddy-page-skipping.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Ye Liu <[email protected]>
Subject: mm/page_owner: extract skip_buddy_pages() helper to unify buddy page skipping
Date: Tue, 14 Jul 2026 09:51:00 +0800

Patch series "mm/page_owner: misc cleanups", v6.

This series collects a few cleanups for mm/page_owner.c that have been accumulated while reading through the file. There is no functional change -- the goal is to make the code easier to read and maintain.

Patch 1 consolidates three identical PageBuddy skip blocks into a single skip_buddy_pages() helper, eliminating the duplication and keeping the lockless-read comment in one place.

Patch 2 replaces the -1 magic number used for "never migrated" with a proper MR_NEVER member in enum migrate_reason, adds the corresponding "never_migrated" string in the MIGRATE_REASON trace macro, and updates the GDB page_owner script to use MR_NEVER so that lx-dump-page-owner correctly detects unmigrated pages.

Patch 3 follows up by converting the remaining 'int reason' parameters throughout the migration and hugetlb callchains to 'enum migrate_reason', making the type explicit and gaining compiler checking. The 'short last_migrate_reason' struct field in page_owner is intentionally left as 'short' since it is per-page metadata where size matters.

Patch 4 hoists the CONFIG_MEMCG guard out of print_page_owner_memcg()'s body so that the real implementation and the empty stub are two clearly separate definitions, the common kernel idiom.

Patch 5 adds a missing \n to the count_threshold debugfs attribute format string so that cat(1) output is properly terminated.

Patch 6 moves free_ts_nsec from the allocation summary line to the free section in __dump_page_owner(), grouping it with free_pid and free_tgid where it logically belongs. This also makes the dump output consistent with print_page_owner().

Patch 7 drops the redundant page_owner_ prefix from file-scoped static symbols (stack_fops, threshold_fops, etc.). Since they cannot collide across translation units, the prefix carries no information.

Patch 8 clamps the PFN advance in skip_buddy_pages() at the next MAX_ORDER_NR_PAGES boundary. The lockless buddy_order_unsafe() read can return a garbage order value if the page is concurrently allocated between the PageBuddy check and the private read, potentially causing the PFN to advance past the next bounadry whose pfn_valid() check would have caught an offline memory section. In read_page_owner(), which relies solely on boundary-aligned pfn_valid() to guard pfn_to_page(), this could lead to an unmapped mem_section access.

Patch 9 avoids two TOCTOU issues in print_page_owner_memcg() by reusing the page->memcg_data snapshot already taken via READ_ONCE at the top of the function throughout, instead of calling page_memcg_check() and PageMemcgKmem() which re-read page->memcg_data locklessly with VM_BUG_ON assertions. If the page is concurrently freed and reallocated as a THP tail or slab page between the initial guards and these later calls, those assertions can fire on CONFIG_DEBUG_VM=y builds. The OBJEXTS (slab) case is also simplified with an early return since objcg != memcg for slabs.

This patch (of 6):

Three places in page_owner.c duplicate the same pattern: check if a page is PageBuddy, read its order via buddy_order_unsafe(), advance the pfn past the buddy block if the order is valid, and continue.

Consolidate them into a single inline helper skip_buddy_pages(). The function returns true (skip) for any buddy page and advances @pfn past the block when the order is valid; returns false if the page is not a buddy page and should be processed normally.

The old init_pages_in_zone() variant used "order > 0" as an extra guard before advancing pfn, but the continue was unconditional and (1UL << 0) - 1 == 0, so the behaviour is identical. The comment about zone->lock is preserved in the helper's kernel-doc.

No functional change.

---

 mm/page_owner.c |   52 +++++++++++++++++++++++-----------------------
 1 file changed, 26 insertions(+), 26 deletions(-)

@@ -422,6 +422,29 @@ void __folio_copy_owner(struct folio *ne
 	rcu_read_unlock();
 }
 
+/*
+ * Check if a page is a buddy page and advance @pfn past the entire buddy block.
+ * This safely reads the buddy order without the zone lock, which may cause us
+ * to skip less than the full buddy block, but that is acceptable for page owner
+ * iteration purposes.
+ *
+ * Return: true if the page was skipped (caller should continue its loop),
+ *         false if the page is not a buddy page and should be processed normally.
+ */
+static inline bool skip_buddy_pages(unsigned long *pfn, struct page *page)
+{
+	unsigned long order;
+
+	if (!PageBuddy(page))
+		return false;
+
+	order = buddy_order_unsafe(page);
+	if (order <= MAX_PAGE_ORDER)
+		*pfn += (1UL << order) - 1;
+
+	return true;
+}
+
 void pagetypeinfo_showmixedcount_print(struct seq_file *m,
 				       pg_data_t *pgdat, struct zone *zone)
 {

@@ -461,14 +484,8 @@ void pagetypeinfo_showmixedcount_print(s
 			if (page_zone(page) != zone)
 				continue;
 
-			if (PageBuddy(page)) {
-				unsigned long freepage_order;
-
-				freepage_order = buddy_order_unsafe(page);
-				if (freepage_order <= MAX_PAGE_ORDER)
-					pfn += (1UL << freepage_order) - 1;
+			if (skip_buddy_pages(&pfn, page))
 				continue;
-			}
 
 			if (PageReserved(page))
 				continue;

@@ -697,13 +714,8 @@ read_page_owner(struct file *file, char
 		}
 
 		page = pfn_to_page(pfn);
-		if (PageBuddy(page)) {
-			unsigned long freepage_order = buddy_order_unsafe(page);
-
-			if (freepage_order <= MAX_PAGE_ORDER)
-				pfn += (1UL << freepage_order) - 1;
+		if (skip_buddy_pages(&pfn, page))
 			continue;
-		}
 
 		page_ext = page_ext_get(page);
 		if (unlikely(!page_ext))

@@ -798,20 +810,8 @@ static void init_pages_in_zone(struct zo
 			if (page_zone(page) != zone)
 				continue;
 
-			/*
-			 * To avoid having to grab zone->lock, be a little
-			 * careful when reading buddy page order. The only
-			 * danger is that we skip too much and potentially miss
-			 * some early allocated pages, which is better than
-			 * heavy lock contention.
-			 */
-			if (PageBuddy(page)) {
-				unsigned long order = buddy_order_unsafe(page);
-
-				if (order > 0 && order <= MAX_PAGE_ORDER)
-					pfn += (1UL << order) - 1;
+			if (skip_buddy_pages(&pfn, page))
 				continue;
-			}
 
 			if (PageReserved(page))
 				continue;

_

Patches currently in -mm which might be from [email protected] are