mm: introduce CONFIG_NUMA_MIGRATION and simplify CONFIG_MIGRATION

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.

Link: https://lkml.kernel.org/r/20260319-config_migration-v1-2-42270124966f@kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index 96987d9d95a821f9b1fc3143aaa7ee91b5f4044c..7999c58629eebc864a22372f0e89ea8ae561d001 100644 (file)
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -52,7 +52,7 @@ int mt_perf_to_adistance(struct access_coordinate *perf, int *adist);
 struct memory_dev_type *mt_find_alloc_memory_type(int adist,
                                                  struct list_head *memory_types);
 void mt_put_memory_types(struct list_head *memory_types);
-#ifdef CONFIG_MIGRATION
+#ifdef CONFIG_NUMA_MIGRATION
 int next_demotion_node(int node, const nodemask_t *allowed_mask);
 void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
 bool node_is_toptier(int node);

diff --git a/init/Kconfig b/init/Kconfig
index 444ce811ea674a402db3056bcf3784db78fe13e0..3648e401b78b460803b6804d9d826f615defd935 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -997,7 +997,7 @@ config NUMA_BALANCING
        bool "Memory placement aware NUMA scheduler"
        depends on ARCH_SUPPORTS_NUMA_BALANCING
        depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
-       depends on SMP && NUMA && MIGRATION && !PREEMPT_RT
+       depends on SMP && NUMA_MIGRATION && !PREEMPT_RT
        help
          This option adds support for automatic NUMA aware memory/task placement.
          The mechanism is quite primitive and is based on migrating memory when

diff --git a/mm/Kconfig b/mm/Kconfig
index b2e21d873d3f9aa74ca7d53137eaa09e3907bd26..bd283958d6754add9c265604f36aa7deff2bbecf 100644 (file)
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -627,20 +627,20 @@ config PAGE_REPORTING
          those pages to another entity, such as a hypervisor, so that the
          memory can be freed within the host for other uses.
 
-#
-# support for page migration
-#
-config MIGRATION
-       bool "Page migration"
+config NUMA_MIGRATION
+       bool "NUMA page migration"
        default y
-       depends on (NUMA || MEMORY_HOTREMOVE || COMPACTION || CMA) && MMU
-       help
-         Allows the migration of the physical location of pages of processes
-         while the virtual addresses are not changed. This is useful in
-         two situations. The first is on NUMA systems to put pages nearer
-         to the processors accessing. The second is when allocating huge
-         pages as migration can relocate pages to satisfy a huge page
-         allocation instead of reclaiming.
+       depends on NUMA && MMU
+       select MIGRATION
+       help
+         Support the migration of pages to other NUMA nodes, available to
+         user space through interfaces like migrate_pages(), move_pages(),
+         and mbind(). Selecting this option also enables support for page
+         demotion for memory tiering.
+
+config MIGRATION
+       bool
+       depends on MMU
 
 config DEVICE_MIGRATION
        def_bool MIGRATION && ZONE_DEVICE

diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 986f809376ebdecf47afc5bd94df30e922994bf9..54851d8a195b030e30283a772f330bcac63a04cb 100644 (file)
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -69,7 +69,7 @@ bool folio_use_access_time(struct folio *folio)
 }
 #endif
 
-#ifdef CONFIG_MIGRATION
+#ifdef CONFIG_NUMA_MIGRATION
 static int top_tier_adistance;
 /*
  * node_demotion[] examples:
@@ -129,7 +129,7 @@ static int top_tier_adistance;
  *
  */
 static struct demotion_nodes *node_demotion __read_mostly;
-#endif /* CONFIG_MIGRATION */
+#endif /* CONFIG_NUMA_MIGRATION */
 
 static BLOCKING_NOTIFIER_HEAD(mt_adistance_algorithms);
 
@@ -273,7 +273,7 @@ static struct memory_tier *__node_get_memory_tier(int node)
                                     lockdep_is_held(&memory_tier_lock));
 }
 
-#ifdef CONFIG_MIGRATION
+#ifdef CONFIG_NUMA_MIGRATION
 bool node_is_toptier(int node)
 {
        bool toptier;
@@ -519,7 +519,7 @@ static void establish_demotion_targets(void)
 
 #else
 static inline void establish_demotion_targets(void) {}
-#endif /* CONFIG_MIGRATION */
+#endif /* CONFIG_NUMA_MIGRATION */
 
 static inline void __init_node_memory_type(int node, struct memory_dev_type *memtype)
 {
@@ -911,7 +911,7 @@ static int __init memory_tier_init(void)
        if (ret)
                panic("%s() failed to register memory tier subsystem\n", __func__);
 
-#ifdef CONFIG_MIGRATION
+#ifdef CONFIG_NUMA_MIGRATION
        node_demotion = kzalloc_objs(struct demotion_nodes, nr_node_ids);
        WARN_ON(!node_demotion);
 #endif
@@ -938,7 +938,7 @@ subsys_initcall(memory_tier_init);
 
 bool numa_demotion_enabled = false;
 
-#ifdef CONFIG_MIGRATION
+#ifdef CONFIG_NUMA_MIGRATION
 #ifdef CONFIG_SYSFS
 static ssize_t demotion_enabled_show(struct kobject *kobj,
                                     struct kobj_attribute *attr, char *buf)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index e5528c35bbb8a4fa8964738e8b74b051bc044347..fd08771e2057b3e5de533d49454a6e014231917e 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1239,7 +1239,7 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
        return err;
 }
 
-#ifdef CONFIG_MIGRATION
+#ifdef CONFIG_NUMA_MIGRATION
 static bool migrate_folio_add(struct folio *folio, struct list_head *foliolist,
                                unsigned long flags)
 {

diff --git a/mm/migrate.c b/mm/migrate.c
index 3323fc96b1cdd23a43a2a3e2ff742188b5efba14..4241eb6eca00fcd8e9ae7801d2f1b285ad1de918 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2222,8 +2222,7 @@ struct folio *alloc_migration_target(struct folio *src, unsigned long private)
        return __folio_alloc(gfp_mask, order, nid, mtc->nmask);
 }
 
-#ifdef CONFIG_NUMA
-
+#ifdef CONFIG_NUMA_MIGRATION
 static int store_status(int __user *status, int start, int value, int nr)
 {
        while (nr-- > 0) {
@@ -2622,6 +2621,7 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
 {
        return kernel_move_pages(pid, nr_pages, pages, nodes, status, flags);
 }
+#endif /* CONFIG_NUMA_MIGRATION */
 
 #ifdef CONFIG_NUMA_BALANCING
 /*
@@ -2764,4 +2764,3 @@ int migrate_misplaced_folio(struct folio *folio, int node)
        return nr_remaining ? -EAGAIN : 0;
 }
 #endif /* CONFIG_NUMA_BALANCING */
-#endif /* CONFIG_NUMA */