Re: [PATCH v2 21/23] mm: rename CONFIG_BALLOON_COMPACTION to CONFIG_BALLOON_MIGRATION

Lorenzo Stoakes
2026-01-15T13:53:23Z

On Thu, Jan 15, 2026 at 10:20:11AM +0100, David Hildenbrand (Red Hat) wrote:
> While compaction depends on migration, the other direction is not the
> case. So let's make it clearer that this is all about migration of
> balloon pages.
>
> Adjust all comments/docs in the core to talk about "migration" instead
> of "compaction".

Saw:

include/linux/balloon.h:25: * performing balloon page compaction. In order to sort out these racy scenarios
include/linux/balloon.h:26: * and safely perform balloon's page compaction and migration we must, always,
Documentation/mm/page_migration.rst:175:balloon-compaction infrastructure residing in the core kernel.

At this commit so maybe a few more to chase up?

>
> While at it add some "/* CONFIG_BALLOON_MIGRATION */".
>
> Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>

Otherwise LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
> Documentation/admin-guide/mm/memory-hotplug.rst | 8 ++++----
> arch/powerpc/platforms/pseries/cmm.c | 8 ++++----
> drivers/misc/vmw_balloon.c | 8 ++++----
> drivers/virtio/virtio_balloon.c | 6 +++---
> include/linux/balloon.h | 2 +-
> include/linux/vm_event_item.h | 4 ++--
> mm/Kconfig | 4 ++--
> mm/balloon.c | 10 +++++-----
> mm/memory_hotplug.c | 4 ++--
> mm/migrate.c | 2 +-
> mm/vmstat.c | 4 ++--
> 11 files changed, 30 insertions(+), 30 deletions(-)
>
> diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
> index 6581558fd0d7a..0207f87251421 100644
> --- a/Documentation/admin-guide/mm/memory-hotplug.rst
> +++ b/Documentation/admin-guide/mm/memory-hotplug.rst
> @@ -603,11 +603,11 @@ ZONE_MOVABLE, especially when fine-tuning zone ratios:
> memory for metadata and page tables in the direct map; having a lot of offline
> memory blocks is not a typical case, though.
>
> -- Memory ballooning without balloon compaction is incompatible with
> - ZONE_MOVABLE. Only some implementations, such as virtio-balloon and
> - pseries CMM, fully support balloon compaction.
> +- Memory ballooning without support for balloon memory migration is incompatible
> + with ZONE_MOVABLE. Only some implementations, such as virtio-balloon and
> + pseries CMM, fully support balloon memory migration.
>
> - Further, the CONFIG_BALLOON_COMPACTION kernel configuration option might be
> + Further, the CONFIG_BALLOON_MIGRATION kernel configuration option might be
> disabled. In that case, balloon inflation will only perform unmovable
> allocations and silently create a zone imbalance, usually triggered by
> inflation requests from the hypervisor.
> diff --git a/arch/powerpc/platforms/pseries/cmm.c b/arch/powerpc/platforms/pseries/cmm.c
> index 7a3c4922685ab..8d83df12430f2 100644
> --- a/arch/powerpc/platforms/pseries/cmm.c
> +++ b/arch/powerpc/platforms/pseries/cmm.c
> @@ -494,7 +494,7 @@ static struct notifier_block cmm_mem_nb = {
> .priority = CMM_MEM_HOTPLUG_PRI
> };
>
> -#ifdef CONFIG_BALLOON_COMPACTION
> +#ifdef CONFIG_BALLOON_MIGRATION
> static int cmm_migratepage(struct balloon_dev_info *b_dev_info,
> struct page *newpage, struct page *page,
> enum migrate_mode mode)
> @@ -520,10 +520,10 @@ static int cmm_migratepage(struct balloon_dev_info *b_dev_info,
> plpar_page_set_active(page);
> return 0;
> }
> -#else /* CONFIG_BALLOON_COMPACTION */
> +#else /* CONFIG_BALLOON_MIGRATION */
> int cmm_migratepage(struct balloon_dev_info *b_dev_info, struct page *newpage,
> struct page *page, enum migrate_mode mode);
> -#endif /* CONFIG_BALLOON_COMPACTION */
> +#endif /* CONFIG_BALLOON_MIGRATION */
>
> /**
> * cmm_init - Module initialization
> @@ -540,7 +540,7 @@ static int cmm_init(void)
>
> balloon_devinfo_init(&b_dev_info);
> b_dev_info.adjust_managed_page_count = true;
> - if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
> + if (IS_ENABLED(CONFIG_BALLOON_MIGRATION))
> b_dev_info.migratepage = cmm_migratepage;
>
> rc = register_oom_notifier(&cmm_oom_nb);
> diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
> index 7fd3f709108c2..216a163959684 100644
> --- a/drivers/misc/vmw_balloon.c
> +++ b/drivers/misc/vmw_balloon.c
> @@ -1719,7 +1719,7 @@ static inline void vmballoon_debugfs_exit(struct vmballoon *b)
> #endif /* CONFIG_DEBUG_FS */
>
>
> -#ifdef CONFIG_BALLOON_COMPACTION
> +#ifdef CONFIG_BALLOON_MIGRATION
> /**
> * vmballoon_migratepage() - migrates a balloon page.
> * @b_dev_info: balloon device information descriptor.
> @@ -1803,11 +1803,11 @@ static int vmballoon_migratepage(struct balloon_dev_info *b_dev_info,
> up_read(&b->conf_sem);
> return ret;
> }
> -#else /* CONFIG_BALLOON_COMPACTION */
> +#else /* CONFIG_BALLOON_MIGRATION */
> int vmballoon_migratepage(struct balloon_dev_info *b_dev_info,
> struct page *newpage, struct page *page,
> enum migrate_mode mode);
> -#endif /* CONFIG_BALLOON_COMPACTION */
> +#endif /* CONFIG_BALLOON_MIGRATION */
>
> static int __init vmballoon_init(void)
> {
> @@ -1827,7 +1827,7 @@ static int __init vmballoon_init(void)
> return error;
>
> balloon_devinfo_init(&balloon.b_dev_info);
> - if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
> + if (IS_ENABLED(CONFIG_BALLOON_MIGRATION))
> balloon.b_dev_info.migratepage = vmballoon_migratepage;
>
> INIT_LIST_HEAD(&balloon.huge_pages);
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index de8041c3285a1..4e549abe59ff1 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -802,7 +802,7 @@ static void report_free_page_func(struct work_struct *work)
> }
> }
>
> -#ifdef CONFIG_BALLOON_COMPACTION
> +#ifdef CONFIG_BALLOON_MIGRATION
> /*
> * virtballoon_migratepage - perform the balloon page migration on behalf of
> * a compaction thread. (called under page lock)
> @@ -851,7 +851,7 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
> mutex_unlock(&vb->balloon_lock);
> return 0;
> }
> -#endif /* CONFIG_BALLOON_COMPACTION */
> +#endif /* CONFIG_BALLOON_MIGRATION */
>
> static unsigned long shrink_free_pages(struct virtio_balloon *vb,
> unsigned long pages_to_free)
> @@ -948,7 +948,7 @@ static int virtballoon_probe(struct virtio_device *vdev)
>
> 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
> +#ifdef CONFIG_BALLOON_MIGRATION
> vb->vb_dev_info.migratepage = virtballoon_migratepage;
> #endif
> if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> diff --git a/include/linux/balloon.h b/include/linux/balloon.h
> index 82585542300d6..e8da95ca4ad48 100644
> --- a/include/linux/balloon.h
> +++ b/include/linux/balloon.h
> @@ -45,7 +45,7 @@
>
> /*
> * Balloon device information descriptor.
> - * This struct is used to allow the common balloon compaction interface
> + * This struct is used to allow the common balloon page migration interface
> * procedures to find the proper balloon device holding memory pages they'll
> * have to cope for page compaction / migration, as well as it serves the
> * balloon driver as a page book-keeper for its registered balloon devices.
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index 92f80b4d69a6d..fca34d3473b6b 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -125,9 +125,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
> #ifdef CONFIG_MEMORY_BALLOON
> BALLOON_INFLATE,
> BALLOON_DEFLATE,
> -#ifdef CONFIG_BALLOON_COMPACTION
> +#ifdef CONFIG_BALLOON_MIGRATION
> BALLOON_MIGRATE,
> -#endif
> +#endif /* CONFIG_BALLOON_MIGRATION */
> #endif
> #ifdef CONFIG_DEBUG_TLBFLUSH
> NR_TLB_REMOTE_FLUSH, /* cpu tried to flush others' tlbs */
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 0d13c1b36e1c1..460a148d5b71a 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -597,8 +597,8 @@ config MEMORY_BALLOON
> bool
>
> #
> -# support for memory balloon compaction
> -config BALLOON_COMPACTION
> +# support for memory balloon page migration
> +config BALLOON_MIGRATION
> bool "Allow for balloon memory migration"
> default y
> depends on MIGRATION && MEMORY_BALLOON
> diff --git a/mm/balloon.c b/mm/balloon.c
> index 5734dae81e318..8a21c6b9a7f0a 100644
> --- a/mm/balloon.c
> +++ b/mm/balloon.c
> @@ -34,7 +34,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
> {
> lockdep_assert_held(&balloon_pages_lock);
> __SetPageOffline(page);
> - if (IS_ENABLED(CONFIG_BALLOON_COMPACTION)) {
> + if (IS_ENABLED(CONFIG_BALLOON_MIGRATION)) {
> SetPageMovableOps(page);
> set_page_private(page, (unsigned long)balloon);
> }
> @@ -51,7 +51,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
> static inline void balloon_page_finalize(struct page *page)
> {
> lockdep_assert_held(&balloon_pages_lock);
> - if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
> + if (IS_ENABLED(CONFIG_BALLOON_MIGRATION))
> set_page_private(page, 0);
> /* PageOffline is sticky until the page is freed to the buddy. */
> }
> @@ -153,7 +153,7 @@ struct page *balloon_page_alloc(void)
> {
> gfp_t gfp_flags = __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;
>
> - if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
> + if (IS_ENABLED(CONFIG_BALLOON_MIGRATION))
> gfp_flags |= GFP_HIGHUSER_MOVABLE;
> else
> gfp_flags |= GFP_HIGHUSER;
> @@ -232,7 +232,7 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
> }
> EXPORT_SYMBOL_GPL(balloon_page_dequeue);
>
> -#ifdef CONFIG_BALLOON_COMPACTION
> +#ifdef CONFIG_BALLOON_MIGRATION
>
> static bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
>
> @@ -340,4 +340,4 @@ static int __init balloon_init(void)
> }
> core_initcall(balloon_init);
>
> -#endif /* CONFIG_BALLOON_COMPACTION */
> +#endif /* CONFIG_BALLOON_MIGRATION */
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 389989a28abe0..bc805029da517 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -946,8 +946,8 @@ static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn
> * We rely on "present pages" instead of "managed pages", as the latter is
> * highly unreliable and dynamic in virtualized environments, and does not
> * consider boot time allocations. For example, memory ballooning adjusts the
> - * managed pages when inflating/deflating the balloon, and balloon compaction
> - * can even migrate inflated pages between zones.
> + * managed pages when inflating/deflating the balloon, and balloon page
> + * migration can even migrate inflated pages between zones.
> *
> * Using "present pages" is better but some things to keep in mind are:
> *
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 4750a2ba15fef..1bf2cf8c44dd4 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -88,7 +88,7 @@ static const struct movable_operations *page_movable_ops(struct page *page)
> * back to the buddy.
> */
> if (PageOffline(page))
> - /* Only balloon compaction sets PageOffline pages movable. */
> + /* Only balloon page migration sets PageOffline pages movable. */
> return offline_movable_ops;
> if (PageZsmalloc(page))
> return zsmalloc_movable_ops;
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 6ae8891c9693e..e96a344ab5974 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1422,9 +1422,9 @@ const char * const vmstat_text[] = {
> #ifdef CONFIG_MEMORY_BALLOON
> [I(BALLOON_INFLATE)] = "balloon_inflate",
> [I(BALLOON_DEFLATE)] = "balloon_deflate",
> -#ifdef CONFIG_BALLOON_COMPACTION
> +#ifdef CONFIG_BALLOON_MIGRATION
> [I(BALLOON_MIGRATE)] = "balloon_migrate",
> -#endif
> +#endif /* CONFIG_BALLOON_MIGRATION */
> #endif /* CONFIG_MEMORY_BALLOON */
> #ifdef CONFIG_DEBUG_TLBFLUSH
> [I(NR_TLB_REMOTE_FLUSH)] = "nr_tlb_remote_flush",
> --
> 2.52.0
>