[PATCH v2 05/23] mm/balloon_compaction: centralize adjust_managed_page_count() handling

David Hildenbrand (Red Hat)
2026-01-15T09:21:06Z

Let's centralize it, by allowing for the driver to enable this handling
through a new flag (bool for now) in the balloon device info.

Note that we now adjust the counter when adding/removing a page into the
balloon list: when removing a page to deflate it, it will now happen
before the driver communicated with hypervisor, not afterwards.

This shouldn't make a difference in practice.

Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
---
arch/powerpc/platforms/pseries/cmm.c | 13 +------------
drivers/virtio/virtio_balloon.c | 19 ++-----------------
include/linux/balloon_compaction.h | 2 ++
mm/balloon_compaction.c | 17 +++++++++++++++++
4 files changed, 22 insertions(+), 29 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/cmm.c b/arch/powerpc/platforms/pseries/cmm.c
index 15f873f733a41..7fd8b3d7e7637 100644
--- a/arch/powerpc/platforms/pseries/cmm.c
+++ b/arch/powerpc/platforms/pseries/cmm.c
@@ -165,7 +165,6 @@ static long cmm_alloc_pages(long nr)

balloon_page_enqueue(&b_dev_info, page);
atomic_long_inc(&loaned_pages);
- adjust_managed_page_count(page, -1);
nr--;
}

@@ -190,7 +189,6 @@ static long cmm_free_pages(long nr)
if (!page)
break;
plpar_page_set_active(page);
- adjust_managed_page_count(page, 1);
__free_page(page);
atomic_long_dec(&loaned_pages);
nr--;
@@ -515,16 +513,6 @@ static int cmm_migratepage(struct balloon_dev_info *b_dev_info,
return -EBUSY;
}

- /*
- * When we migrate a page to a different zone, we have to fixup the
- * count of both involved zones as we adjusted the managed page count
- * when inflating.
- */
- if (page_zone(page) != page_zone(newpage)) {
- adjust_managed_page_count(page, 1);
- adjust_managed_page_count(newpage, -1);
- }
-
/*
* activate/"deflate" the old page. We ignore any errors just like the
* other callers.
@@ -551,6 +539,7 @@ static int cmm_init(void)
return -EOPNOTSUPP;

balloon_devinfo_init(&b_dev_info);
+ b_dev_info.adjust_managed_page_count = true;
if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
b_dev_info.migratepage = cmm_migratepage;

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index df2756c071dae..15c1cf5fd249c 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -274,9 +274,6 @@ static unsigned int fill_balloon(struct virtio_balloon *vb, size_t num)

set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
- if (!virtio_has_feature(vb->vdev,
- VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
- adjust_managed_page_count(page, -1);
vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
}

@@ -295,9 +292,6 @@ static void release_pages_balloon(struct virtio_balloon *vb,
struct page *page, *next;

list_for_each_entry_safe(page, next, pages, lru) {
- if (!virtio_has_feature(vb->vdev,
- VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
- adjust_managed_page_count(page, 1);
list_del(&page->lru);
put_page(page); /* balloon reference */
}
@@ -839,17 +833,6 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
if (!mutex_trylock(&vb->balloon_lock))
return -EAGAIN;

- /*
- * When we migrate a page to a different zone and adjusted the
- * managed page count when inflating, we have to fixup the count of
- * both involved zones.
- */
- if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM) &&
- page_zone(page) != page_zone(newpage)) {
- adjust_managed_page_count(page, 1);
- adjust_managed_page_count(newpage, -1);
- }
-
/* balloon's page migration 1st step -- inflate "newpage" */
vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
set_page_pfns(vb, vb->pfns, newpage);
@@ -958,6 +941,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
if (err)
goto out_free_vb;

+ if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+ vb->vb_dev_info.adjust_managed_page_count = true;
#ifdef CONFIG_BALLOON_COMPACTION
vb->vb_dev_info.migratepage = virtballoon_migratepage;
#endif
diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
index 7cfe48769239e..3109d3c43d306 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -56,6 +56,7 @@ struct balloon_dev_info {
struct list_head pages; /* Pages enqueued & handled to Host */
int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
struct page *page, enum migrate_mode mode);
+ bool adjust_managed_page_count;
};

extern struct page *balloon_page_alloc(void);
@@ -73,6 +74,7 @@ static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
spin_lock_init(&balloon->pages_lock);
INIT_LIST_HEAD(&balloon->pages);
balloon->migratepage = NULL;
+ balloon->adjust_managed_page_count = false;
}

#ifdef CONFIG_BALLOON_COMPACTION
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 5444c61bb9e76..fd9ec47cf4670 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -23,6 +23,8 @@ static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
BUG_ON(!trylock_page(page));
balloon_page_insert(b_dev_info, page);
unlock_page(page);
+ if (b_dev_info->adjust_managed_page_count)
+ adjust_managed_page_count(page, -1);
__count_vm_event(BALLOON_INFLATE);
inc_node_page_state(page, NR_BALLOON_PAGES);
}
@@ -95,6 +97,8 @@ size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
continue;

list_del(&page->lru);
+ if (b_dev_info->adjust_managed_page_count)
+ adjust_managed_page_count(page, 1);
balloon_page_finalize(page);
__count_vm_event(BALLOON_DEFLATE);
list_add(&page->lru, pages);
@@ -256,12 +260,25 @@ static int balloon_page_migrate(struct page *newpage, struct page *page,

balloon_page_insert(b_dev_info, newpage);
__count_vm_event(BALLOON_MIGRATE);
+
+ if (b_dev_info->adjust_managed_page_count &&
+ page_zone(page) != page_zone(newpage)) {
+ /*
+ * When we migrate a page to a different zone we
+ * have to fixup the count of both involved zones.
+ */
+ adjust_managed_page_count(page, 1);
+ adjust_managed_page_count(newpage, -1);
+ }
break;
case -ENOENT:
spin_lock_irqsave(&b_dev_info->pages_lock, flags);

/* Old page was deflated but new page not inflated. */
__count_vm_event(BALLOON_DEFLATE);
+
+ if (b_dev_info->adjust_managed_page_count)
+ adjust_managed_page_count(page, 1);
break;
default:
return rc;
--
2.52.0