On 02.07.25 12:34, Harry Yoo wrote:

On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote:

quoted

... instead, look them up statically based on the page type. Maybe in the
future we want a registration interface? At least for now, it can be
easily handled using the two page types that actually support page
migration.

The remaining usage of page->mapping is to flag such pages as actually
being movable (having movable_ops), which we will change next.

Reviewed-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: David Hildenbrand <redacted>
---

quoted

+static const struct movable_operations *page_movable_ops(struct page *page)
+{
+	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
+
+	/*
+	 * If we enable page migration for a page of a certain type by marking
+	 * it as movable, the page type must be sticky until the page gets freed
+	 * back to the buddy.
+	 */
+#ifdef CONFIG_BALLOON_COMPACTION
+	if (PageOffline(page))
+		/* Only balloon compaction sets PageOffline pages movable. */
+		return &balloon_mops;
+#endif /* CONFIG_BALLOON_COMPACTION */
+#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
+	if (PageZsmalloc(page))
+		return &zsmalloc_mops;
+#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */

What happens if:
   CONFIG_ZSMALLOC=y
   CONFIG_TRANSPARENT_HUGEPAGE=n
   CONFIG_COMPACTION=n
   CONFIG_MIGRATION=y

Pages are never allocated from ZONE_MOVABLE/CMA and are not marked as 
having movable_ops, so we never end up in this function. See how 
zsmalloc.c deals with CONFIG_COMPACTION, especially how 
SetZsPageMovable() is a NOP without it.

As a side note, both should probably be moved from COMPACTION to 
MIGRATION. Although probably in practice, anybody enabling 
CONFIG_MIGRATION likely also enables CONFIG_COMPACTION.

-- 
Cheers,

David / dhildenb