On 21.10.25 22:52, Michael S. Tsirkin wrote:
On Tue, Oct 21, 2025 at 02:59:12PM +0200, David Hildenbrand wrote:
In order to remove the dependency on the page lock for balloon
pages, we need a lock that is independent of the page.
It's crucial that we can handle the scenario where balloon deflation
(clearing page->private) can race with page isolation (using
page->private to obtain the balloon_dev_info where the lock currently
resides).
The current lock in balloon_dev_info is therefore not suitable.
Fortunately, we never really have more than a single balloon device
per VM, so we can just keep it simple and use a static lock to protect
all balloon devices.
Based on this change we will remove the dependency on the page lock
next.
Signed-off-by: David Hildenbrand <[email protected]>
---
include/linux/balloon_compaction.h | 6 ++---
mm/balloon_compaction.c | 36 +++++++++++++++++-------------
2 files changed, 23 insertions(+), 19 deletions(-)
diff --git a/include/linux/balloon_compaction.h
b/include/linux/balloon_compaction.h
index 3109d3c43d306..e2d9eb40e1fbb 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -21,10 +21,10 @@
* i. Setting the PG_movable_ops flag and page->private with the following
* lock order
* +-page_lock(page);
- * +--spin_lock_irq(&b_dev_info->pages_lock);
+ * +--spin_lock_irq(&balloon_pages_lock);
*
* ii. isolation or dequeueing procedure must remove the page from balloon
- * device page list under b_dev_info->pages_lock.
+ * device page list under &balloon_pages_lock
Using &balloon_pages_lock with an & is kinda weird here.
Indeed, fixed, thanks!
--
Cheers
David / dhildenb
