linux-kernel - Re: [PATCH v1 20/23] mm/kconfig: make BALLOON

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Message-ID: <3ba11b0c-818f-41d5-8885-038c7e0133f5@infradead.org>
Date: Tue, 21 Oct 2025 10:13:33 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc: 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>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "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 v1 20/23] mm/kconfig: make BALLOON_COMPACTION depend on
 MIGRATION

On 10/21/25 8:00 AM, David Hildenbrand 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 <david@...hat.com>
> ---
>  mm/Kconfig | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index e47321051d765..3aff4d05a2d8c 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 get

nit:
s/get/be/

> +	  migrated for memory defragmentation purposes by memory compaction.
>  
>  #
>  # support for memory compaction

-- 
~Randy