mm: add a helper to accept page

Accept a given struct page and add it free list.

The help is useful for physical memory scanners that want to use free
unaccepted memory.

Link: https://lkml.kernel.org/r/20240809114854.3745464-7-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/internal.h

@@ -1432,4 +1432,12 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 	unsigned long new_addr, unsigned long len,
 	bool need_rmap_locks, bool for_stack);
 
+#ifdef CONFIG_UNACCEPTED_MEMORY
+void accept_page(struct page *page);
+#else /* CONFIG_UNACCEPTED_MEMORY */
+static inline void accept_page(struct page *page)
+{
+}
+#endif /* CONFIG_UNACCEPTED_MEMORY */
+
 #endif	/* __MM_INTERNAL_H */

mm/page_alloc.c

@@ -6935,34 +6935,57 @@ static bool page_contains_unaccepted(struct page *page, unsigned int order)
 	return range_contains_unaccepted_memory(start, PAGE_SIZE << order);
 }
 
-static bool try_to_accept_memory_one(struct zone *zone)
+static void __accept_page(struct zone *zone, unsigned long *flags,
+			  struct page *page)
 {
-	unsigned long flags;
-	struct page *page;
 	bool last;
 
-	spin_lock_irqsave(&zone->lock, flags);
-	page = list_first_entry_or_null(&zone->unaccepted_pages,
-					struct page, lru);
-	if (!page) {
-		spin_unlock_irqrestore(&zone->lock, flags);
-		return false;
-	}
-
 	list_del(&page->lru);
 	last = list_empty(&zone->unaccepted_pages);
 
 	account_freepages(zone, -MAX_ORDER_NR_PAGES, MIGRATE_MOVABLE);
 	__mod_zone_page_state(zone, NR_UNACCEPTED, -MAX_ORDER_NR_PAGES);
 	__ClearPageUnaccepted(page);
-	spin_unlock_irqrestore(&zone->lock, flags);
+	spin_unlock_irqrestore(&zone->lock, *flags);
 
 	accept_memory(page_to_phys(page), PAGE_SIZE << MAX_PAGE_ORDER);
 
 	__free_pages_ok(page, MAX_PAGE_ORDER, FPI_TO_TAIL);
 
 	if (last)
 		static_branch_dec(&zones_with_unaccepted_pages);
+}
+
+void accept_page(struct page *page)
+{
+	struct zone *zone = page_zone(page);
+	unsigned long flags;
+
+	spin_lock_irqsave(&zone->lock, flags);
+	if (!PageUnaccepted(page)) {
+		spin_unlock_irqrestore(&zone->lock, flags);
+		return;
+	}
+
+	/* Unlocks zone->lock */
+	__accept_page(zone, &flags, page);
+}
+
+static bool try_to_accept_memory_one(struct zone *zone)
+{
+	unsigned long flags;
+	struct page *page;
+
+	spin_lock_irqsave(&zone->lock, flags);
+	page = list_first_entry_or_null(&zone->unaccepted_pages,
+					struct page, lru);
+	if (!page) {
+		spin_unlock_irqrestore(&zone->lock, flags);
+		return false;
+	}
+
+	/* Unlocks zone->lock */
+	__accept_page(zone, &flags, page);
 
 	return true;
 }