Message-ID: <76a1cf4e-7635-4bba-a350-d6f6da6fbe6e@lucifer.local>
Date: Thu, 15 Jan 2026 13:52:47 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org,
        Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
        linux-doc@...r.kernel.org, virtualization@...ts.linux.dev,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Jonathan Corbet <corbet@....net>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jerrin Shaji George <jerrin.shaji-george@...adcom.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Eugenio Pérez <eperezma@...hat.com>,
        Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH v2 21/23] mm: rename CONFIG_BALLOON_COMPACTION to
 CONFIG_BALLOON_MIGRATION

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@...nel.org>

Otherwise LGTM, so:

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

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