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

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Message-ID: <20251021150040.498160-4-david@redhat.com>
Date: Tue, 21 Oct 2025 17:00:37 +0200
From: David Hildenbrand <david@...hat.com>
To: 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>,
	David Hildenbrand <david@...hat.com>
Subject: [PATCH v1 20/23] mm/kconfig: make BALLOON_COMPACTION depend on MIGRATION

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
+	  migrated for memory defragmentation purposes by memory compaction.
 
 #
 # support for memory compaction
-- 
2.51.0