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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-rt-devel@lists.linux.dev Subject: Re: [PATCH 2/2] mm: introduce CONFIG_NUMA_MIGRATION and simplify CONFIG_MIGRATION Date: Thu, 19 Mar 2026 13:39:09 -0400 X-Mailer: MailMate (2.0r6290) Message-ID: <42DD15DD-9BBD-4A65-AF76-ADEC557AF416@nvidia.com> In-Reply-To: <20260319-config_migration-v1-2-42270124966f@kernel.org> References: <20260319-config_migration-v1-0-42270124966f@kernel.org> <20260319-config_migration-v1-2-42270124966f@kernel.org> Content-Type: text/plain X-ClientProxiedBy: SJ0PR03CA0195.namprd03.prod.outlook.com (2603:10b6:a03:2ef::20) To 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lJUnMBJYVTYlvWdYDi3FCwv2J71GwQLAuiUVfg5qW13OWNE6NUxfK1GSiwJYKlOnWS9kW8Q3XXUcM0jAhCxJRMdFI+BCG1gyN4x7JFtReVAyWQOWCqer9O3T9VBDhGfBLePOH+2eUP8WYoT0uU66Dm/Cn29ojiQkVF4f2WNAqujuCbI6KQyd5y3Qk6rete6S6UVj+gH66kgL1Z90FpLPlXJHuS/TUOLE87r3orBWIZPRClqVERZWKWmNQYs6v4qIEh3cLYxSxnKOGvWQZ0nw7HnSliytrOU7t29I8biYclFi6pl/9GcOwZgHA9AFvM5/KHnk6JI7WP+VMKQfHE+oreX/WB0rn+xpTyoKBCc96X4ftfrYQdSIBhA6rSNi1mN2HiVbL+/8YmAdafmkzzlNRngmgpbccdsrR5zy1o7WMcD3rfzobwxBksG0x7jqI5ha45XGWvv1EUpbn2OkmnyKC1U08jNYh78IpY42XRL9G9UyhHQs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 19 Mar 2026, at 4:19, David Hildenbrand (Arm) wrote: > CONFIG_MEMORY_HOTREMOVE, CONFIG_COMPACTION and CONFIG_CMA all select > CONFIG_MIGRATION, because they require it to work (users). > > Only CONFIG_NUMA_BALANCING and CONFIG_BALLOON_MIGRATION depend on > CONFIG_MIGRATION. CONFIG_BALLOON_MIGRATION is not an actual user, but > an implementation of migration support, so the dependency is correct > (CONFIG_BALLOON_MIGRATION does not make any sense without > CONFIG_MIGRATION). > > However, kconfig-language.rst clearly states "In general use select only > for non-visible symbols". So far CONFIG_MIGRATION is user-visible ... > and the dependencies rather confusing. > > The whole reason why CONFIG_MIGRATION is user-visible is because of > CONFIG_NUMA: some users might want CONFIG_NUMA but not page migration > support. > > Let's clean all that up by introducing a dedicated CONFIG_NUMA_MIGRATION > config option for that purpose only. Make CONFIG_NUMA_BALANCING that so > far depended on CONFIG_NUMA && CONFIG_MIGRATION to depend on > CONFIG_MIGRATION instead. CONFIG_NUMA_MIGRATION will depend on > CONFIG_NUMA && CONFIG_MMU. > > CONFIG_NUMA_MIGRATION is user-visible and will default to "y". We > use that default so new configs will automatically enable it, just > like it was the case with CONFIG_MIGRATION. The downside is that > some configs that used to have CONFIG_MIGRATION=n might get it > re-enabled by CONFIG_NUMA_MIGRATION=y, which shouldn't be a problem. > > CONFIG_MIGRATION is now a non-visible config option. Any code that > select CONFIG_MIGRATION (as before) must depend directly or indirectly > on CONFIG_MMU. > > CONFIG_NUMA_MIGRATION is responsible for any NUMA migration code, which is > mempolicy migration code, memory-tiering code, and move_pages() code in > migrate.c. CONFIG_NUMA_BALANCING uses its functionality. > > Note that this implies that with CONFIG_NUMA_MIGRATION=n, move_pages() will > not be available even though CONFIG_MIGRATION=y, which is an expected > change. > > In migrate.c, we can remove the CONFIG_NUMA check as both > CONFIG_NUMA_MIGRATION and CONFIG_NUMA_BALANCING depend on it. > > With this change, CONFIG_MIGRATION is an internal config, all users of > migration selects CONFIG_MIGRATION, and only CONFIG_BALLOON_MIGRATION > depends on it. > > Signed-off-by: David Hildenbrand (Arm) > --- > include/linux/memory-tiers.h | 2 +- > init/Kconfig | 2 +- > mm/Kconfig | 26 +++++++++++++------------- > mm/memory-tiers.c | 12 ++++++------ > mm/mempolicy.c | 2 +- > mm/migrate.c | 5 ++--- > 6 files changed, 24 insertions(+), 25 deletions(-) > LGTM. Acked-by: Zi Yan Best Regards, Yan, Zi