[PATCH v1 02/29] mm/balloon_compaction: convert balloon_page_delete() to balloon_page_finalize()

David Hildenbrand
2025-06-30T13:01:29Z

Let's move the removal of the page from the balloon list into the single
caller, to remove the dependency on the PG_isolated flag and clarify
locking requirements.

We'll shuffle the operations a bit such that they logically make more sense
(e.g., remove from the list before clearing flags).

In balloon migration functions we can now move the balloon_page_finalize()
out of the balloon lock and perform the finalization just before dropping
the balloon reference.

Document that the page lock is currently required when modifying the
movability aspects of a page; hopefully we can soon decouple this from the
page lock.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
arch/powerpc/platforms/pseries/cmm.c | 2 +-
drivers/misc/vmw_balloon.c | 3 +-
drivers/virtio/virtio_balloon.c | 4 +--
include/linux/balloon_compaction.h | 43 +++++++++++-----------------
mm/balloon_compaction.c | 3 +-
5 files changed, 21 insertions(+), 34 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/cmm.c b/arch/powerpc/platforms/pseries/cmm.c
index 5f4037c1d7fe8..5e0a718d1be7b 100644
--- a/arch/powerpc/platforms/pseries/cmm.c
+++ b/arch/powerpc/platforms/pseries/cmm.c
@@ -532,7 +532,6 @@ static int cmm_migratepage(struct balloon_dev_info *b_dev_info,

spin_lock_irqsave(&b_dev_info->pages_lock, flags);
balloon_page_insert(b_dev_info, newpage);
- balloon_page_delete(page);
b_dev_info->isolated_pages--;
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);

@@ -542,6 +541,7 @@ static int cmm_migratepage(struct balloon_dev_info *b_dev_info,
*/
plpar_page_set_active(page);

+ balloon_page_finalize(page);
/* balloon page list reference */
put_page(page);

diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
index c817d8c216413..6653fc53c951c 100644
--- a/drivers/misc/vmw_balloon.c
+++ b/drivers/misc/vmw_balloon.c
@@ -1778,8 +1778,7 @@ static int vmballoon_migratepage(struct balloon_dev_info *b_dev_info,
* @pages_lock . We keep holding @comm_lock since we will need it in a
* second.
*/
- balloon_page_delete(page);
-
+ balloon_page_finalize(page);
put_page(page);

/* Inflate */
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 89da052f4f687..e299e18346a30 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -866,15 +866,13 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
tell_host(vb, vb->inflate_vq);

/* balloon's page migration 2nd step -- deflate "page" */
- spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
- balloon_page_delete(page);
- spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
set_page_pfns(vb, vb->pfns, page);
tell_host(vb, vb->deflate_vq);

mutex_unlock(&vb->balloon_lock);

+ balloon_page_finalize(page);
put_page(page); /* balloon reference */

return MIGRATEPAGE_SUCCESS;
diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
index 5ca2d56996201..b9f19da37b089 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -97,27 +97,6 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
list_add(&page->lru, &balloon->pages);
}

-/*
- * balloon_page_delete - delete a page from balloon's page list and clear
- * the page->private assignement accordingly.
- * @page : page to be released from balloon's page list
- *
- * Caller must ensure the page is locked and the spin_lock protecting balloon
- * pages list is held before deleting a page from the balloon device.
- */
-static inline void balloon_page_delete(struct page *page)
-{
- __ClearPageOffline(page);
- __ClearPageMovable(page);
- set_page_private(page, 0);
- /*
- * No touch page.lru field once @page has been isolated
- * because VM is using the field.
- */
- if (!PageIsolated(page))
- list_del(&page->lru);
-}
-
/*
* balloon_page_device - get the b_dev_info descriptor for the balloon device
* that enqueues the given page.
@@ -141,12 +120,6 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
list_add(&page->lru, &balloon->pages);
}

-static inline void balloon_page_delete(struct page *page)
-{
- __ClearPageOffline(page);
- list_del(&page->lru);
-}
-
static inline gfp_t balloon_mapping_gfp_mask(void)
{
return GFP_HIGHUSER;
@@ -154,6 +127,22 @@ static inline gfp_t balloon_mapping_gfp_mask(void)

#endif /* CONFIG_BALLOON_COMPACTION */

+/*
+ * balloon_page_finalize - prepare a balloon page that was removed from the
+ * balloon list for release to the page allocator
+ * @page: page to be released to the page allocator
+ *
+ * Caller must ensure that the page is locked.
+ */
+static inline void balloon_page_finalize(struct page *page)
+{
+ if (IS_ENABLED(CONFIG_BALLOON_COMPACTION)) {
+ __ClearPageMovable(page);
+ set_page_private(page, 0);
+ }
+ __ClearPageOffline(page);
+}
+
/*
* balloon_page_push - insert a page into a page list.
* @head : pointer to list
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index fcb60233aa35d..ec176bdb8a78b 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -94,7 +94,8 @@ size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
if (!trylock_page(page))
continue;

- balloon_page_delete(page);
+ list_del(&page->lru);
+ balloon_page_finalize(page);
__count_vm_event(BALLOON_DEFLATE);
list_add(&page->lru, pages);
unlock_page(page);
--
2.49.0