On Thu, Mar 19, 2026 at 09:19:41AM +0100, 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.
Nice. I always found it odd that it was optional. > > 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) <[email protected]> AFAICT this all LGTM, so: Reviewed-by: Lorenzo Stoakes (Oracle) <[email protected]> > --- > 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(-) > > diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h > index 96987d9d95a8..7999c58629ee 100644 > --- 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 444ce811ea67..3648e401b78b 100644 > --- 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 b2e21d873d3f..bd283958d675 100644 > --- 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 986f809376eb..54851d8a195b 100644 > --- 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 e5528c35bbb8..fd08771e2057 100644 > --- 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 fdbb20163f66..05cb408846f2 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -2224,8 +2224,7 @@ 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) { > @@ -2624,6 +2623,7 @@ 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 > /* > @@ -2766,4 +2766,3 @@ int migrate_misplaced_folio(struct folio *folio, int > node) > return nr_remaining ? -EAGAIN : 0; > } > #endif /* CONFIG_NUMA_BALANCING */ > -#endif /* CONFIG_NUMA */ > > -- > 2.43.0 >
