mm/balloon_compaction: centralize adjust_managed_page_count() handling

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.

Link: https://lkml.kernel.org/r/20260119230133.3551867-7-david@kernel.org
Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
Acked-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
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: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
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>

1 files changed, 2 insertions, 17 deletions

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index df2756c071da..15c1cf5fd249 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