linux-kernel - [PATCH RFC 13/29] mm/balloon_compaction: stop using _

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Message-ID: <20250618174014.1168640-14-david@redhat.com>
Date: Wed, 18 Jun 2025 19:39:56 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
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Subject: [PATCH RFC 13/29] mm/balloon_compaction: stop using __ClearPageMovable()

We can just look at the balloon device (stored in page->private), to see
of the page is still part of the balloon.

As isolated balloon pages cannot get released (they are taken off the
balloon list while isolated), we don't have to worry about this case in
the putback and migration callback. Add a WARN_ON_ONCE for now.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 include/linux/balloon_compaction.h |  4 +---
 mm/balloon_compaction.c            | 11 +++++++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
index bfc6e50bd004b..9bce8e9f5018c 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -136,10 +136,8 @@ static inline gfp_t balloon_mapping_gfp_mask(void)
  */
 static inline void balloon_page_finalize(struct page *page)
 {
-	if (IS_ENABLED(CONFIG_BALLOON_COMPACTION)) {
-		__ClearPageMovable(page);
+	if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
 		set_page_private(page, 0);
-	}
 	/* PageOffline is sticky until the page is freed to the buddy. */
 }
 
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index ec176bdb8a78b..e4f1a122d786b 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -206,6 +206,9 @@ static bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
 	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
 	unsigned long flags;
 
+	if (!b_dev_info)
+		return false;
+
 	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 	list_del(&page->lru);
 	b_dev_info->isolated_pages++;
@@ -219,6 +222,10 @@ static void balloon_page_putback(struct page *page)
 	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
 	unsigned long flags;
 
+	/* Isolated balloon pages cannot get deflated. */
+	if (WARN_ON_ONCE(!b_dev_info))
+		return;
+
 	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 	list_add(&page->lru, &b_dev_info->pages);
 	b_dev_info->isolated_pages--;
@@ -234,6 +241,10 @@ static int balloon_page_migrate(struct page *newpage, struct page *page,
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 
+	/* Isolated balloon pages cannot get deflated. */
+	if (WARN_ON_ONCE(!balloon))
+		return -EAGAIN;
+
 	return balloon->migratepage(balloon, newpage, page, mode);
 }
 
-- 
2.49.0