linux-kernel - [PATCH v3 04/24] mm/balloon_compaction: improve comments for WARN_ON_ONCE(!b_dev

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Message-ID: <20260119230133.3551867-5-david@kernel.org>
Date: Tue, 20 Jan 2026 00:01:12 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	linuxppc-dev@...ts.ozlabs.org,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	linux-doc@...r.kernel.org,
	virtualization@...ts.linux.dev,
	"David Hildenbrand (Red Hat)" <david@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oscar Salvador <osalvador@...e.de>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jerrin Shaji George <jerrin.shaji-george@...adcom.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Zi Yan <ziy@...dia.com>
Subject: [PATCH v3 04/24] mm/balloon_compaction: improve comments for WARN_ON_ONCE(!b_dev_info)

Let's clarify a bit by extending the comments.

Signed-off-by: David Hildenbrand (Red Hat) <david@...nel.org>
---
 mm/balloon_compaction.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 03c5dbabb1565..85eea88cea083 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -222,7 +222,11 @@ 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. */
+	/*
+	 * When we isolated the page, the page was still inflated in a balloon
+	 * device. As isolated balloon pages cannot get deflated, we still have
+	 * a balloon device here.
+	 */
 	if (WARN_ON_ONCE(!b_dev_info))
 		return;
 
@@ -241,7 +245,11 @@ 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. */
+	/*
+	 * When we isolated the page, the page was still inflated in a balloon
+	 * device. As isolated balloon pages cannot get deflated, we still have
+	 * a balloon device here.
+	 */
 	if (WARN_ON_ONCE(!balloon))
 		return -EAGAIN;
 
-- 
2.52.0