mm/balloon_compaction: improve comments for WARN_ON_ONCE(!b_dev_info)

Let's clarify a bit by extending the comments.

Link: https://lkml.kernel.org/r/20260119230133.3551867-5-david@kernel.org
Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Eugenio Pérez <eperezma@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Jerrin Shaji George <jerrin.shaji-george@broadcom.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 03c5dbabb1565d0460c517d085abde4fbe3215ec..85eea88cea083abfeadc92bb79aaace422d64d48 100644 (file)
--- 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;