linux-kernel - Re: [PATCH v2 20/23] mm/kconfig: make BALLOON

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Message-ID: <c2dd5cb4-9303-489f-bbd8-2a09a16dd973@lucifer.local>
Date: Thu, 15 Jan 2026 13:47:06 +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 20/23] mm/kconfig: make BALLOON_COMPACTION depend on
 MIGRATION

On Thu, Jan 15, 2026 at 10:20:10AM +0100, David Hildenbrand (Red Hat) wrote:
> Migration support for balloon memory depends on MIGRATION not
> COMPACTION. Compaction is simply another user of page migration.
>
> The last dependency on compaction.c was effectively removed with
> commit 3d388584d599 ("mm: convert "movable" flag in page->mapping to a
> page flag"). Ever since, everything for handling movable_ops page
> migration resides in core migration code.
>
> So let's change the dependency and adjust the description +
> help text.
>
> We'll rename BALLOON_COMPACTION separately next.
>
> Signed-off-by: David Hildenbrand (Red Hat) <david@...nel.org>

Far pithier also. LGTM so:

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

> ---
>  mm/Kconfig | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 24a3ff149a1b0..0d13c1b36e1c1 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -599,17 +599,14 @@ config MEMORY_BALLOON
>  #
>  # support for memory balloon compaction
>  config BALLOON_COMPACTION
> -	bool "Allow for balloon memory compaction/migration"
> +	bool "Allow for balloon memory migration"
>  	default y
> -	depends on COMPACTION && MEMORY_BALLOON
> -	help
> -	  Memory fragmentation introduced by ballooning might reduce
> -	  significantly the number of 2MB contiguous memory blocks that can be
> -	  used within a guest, thus imposing performance penalties associated
> -	  with the reduced number of transparent huge pages that could be used
> -	  by the guest workload. Allowing the compaction & migration for memory
> -	  pages enlisted as being part of memory balloon devices avoids the
> -	  scenario aforementioned and helps improving memory defragmentation.
> +	depends on MIGRATION && MEMORY_BALLOON
> +	help
> +	  Allow for migration of pages inflated in a memory balloon such that
> +	  they can be allocated from memory areas only available for movable
> +	  allocations (e.g., ZONE_MOVABLE, CMA) and such that they can be
> +	  migrated for memory defragmentation purposes by memory compaction.
>
>  #
>  # support for memory compaction
> --
> 2.52.0
>