[PATCH 1/6] mm/page_owner: extract skip_buddy_pages() helper to unify buddy page skipping

[Ye Liu <ye.liu@linux.dev>]

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.

Signed-off-by: Ye Liu <ye.liu@linux.dev>
---
 mm/page_owner.c | 52 ++++++++++++++++++++++++-------------------------
 1 file changed, 26 insertions(+), 26 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 2dddcb6510aa..342549891a8d 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -422,6 +422,29 @@ void __folio_copy_owner(struct folio *newfolio, struct folio *old)
 	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(struct seq_file *m,
 			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 __user *buf, size_t count, loff_t *ppos)
 		}
 
 		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 zone *zone)
 			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;
-- 
2.43.0