From: Mike Day <michael.day@xxxxxxx>
Offload-Copy drivers should implement following functions to enable folio
migration offloading:
migrate_offc() - This function takes src and dst folios list undergoing
migration. It is responsible for transfer of page content between the
src and dst folios.
can_migrate_offc() - It performs necessary checks if offload copying
migration is supported for the give src and dst folios.
Offload-Copy driver should include a mechanism to call start_offloading and
stop_offloading for enabling and disabling migration offload respectively.
[Shivank: Rename the APIs and files to generalize the original DMA-specific
offload implementation to support various copy offloading mechanisms such as
DMA engines, CPU multi-threading, or other
hardware accelerators.]
Signed-off-by: Mike Day <michael.day@xxxxxxx>
Signed-off-by: Shivank Garg <shivankg@xxxxxxx>
---
include/linux/migrate_offc.h | 36 +++++++++++++++++++++++++
mm/Kconfig | 8 ++++++
mm/Makefile | 1 +
mm/migrate.c | 43 ++++++++++++++++++++++++++++--
mm/migrate_offc.c | 51 ++++++++++++++++++++++++++++++++++++
5 files changed, 137 insertions(+), 2 deletions(-)
create mode 100644 include/linux/migrate_offc.h
create mode 100644 mm/migrate_offc.c
diff --git a/include/linux/migrate_offc.h b/include/linux/migrate_offc.h
new file mode 100644
index 000000000000..908f81ebd621
--- /dev/null
+++ b/include/linux/migrate_offc.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _MIGRATE_OFFC_H
+#define _MIGRATE_OFFC_H
+#include <linux/migrate_mode.h>
+
+#define MIGRATOR_NAME_LEN 32
+struct migrator {
+ char name[MIGRATOR_NAME_LEN];
+ int (*migrate_offc)(struct list_head *dst_list, struct list_head *src_list, int folio_cnt);
+ bool (*can_migrate_offc)(struct folio *dst, struct folio *src);
+ struct rcu_head srcu_head;
+ struct module *owner;
+};
+
+extern struct migrator migrator;
+extern struct mutex migrator_mut;
+extern struct srcu_struct mig_srcu;
+
+#ifdef CONFIG_OFFC_MIGRATION
+void srcu_mig_cb(struct rcu_head *head);
+void offc_update_migrator(struct migrator *mig);
+unsigned char *get_active_migrator_name(void);
+bool can_offc_migrate(struct folio *dst, struct folio *src);
+void start_offloading(struct migrator *migrator);
+void stop_offloading(void);
+#else
+static inline void srcu_mig_cb(struct rcu_head *head) { };
+static inline void offc_update_migrator(struct migrator *mig) { };
+static inline unsigned char *get_active_migrator_name(void) { return NULL; };
+static inline bool can_offc_migrate(struct folio *dst, struct folio *src) {return true; };
+static inline void start_offloading(struct migrator *migrator) { };
+static inline void stop_offloading(void) { };
+#endif /* CONFIG_OFFC_MIGRATION */
+
+#endif /* _MIGRATE_OFFC_H */
diff --git a/mm/Kconfig b/mm/Kconfig
index 1b501db06417..7a0693c3be4e 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -722,6 +722,14 @@ config MIGRATION
config DEVICE_MIGRATION
def_bool MIGRATION && ZONE_DEVICE
+config OFFC_MIGRATION
+ bool "Migrate Pages offloading copy"
+ def_bool n
+ depends on MIGRATION
+ help
+ An interface allowing external modules or driver to offload
+ page copying in page migration.
+
config ARCH_ENABLE_HUGEPAGE_MIGRATION
bool
diff --git a/mm/Makefile b/mm/Makefile
index 850386a67b3e..010142414176 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -93,6 +93,7 @@ obj-$(CONFIG_FAILSLAB) += failslab.o
obj-$(CONFIG_FAIL_PAGE_ALLOC) += fail_page_alloc.o
obj-$(CONFIG_MEMTEST) += memtest.o
obj-$(CONFIG_MIGRATION) += migrate.o
+obj-$(CONFIG_OFFC_MIGRATION) += migrate_offc.o
obj-$(CONFIG_NUMA) += memory-tiers.o
obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o
obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o
diff --git a/mm/migrate.c b/mm/migrate.c
index 8b6cfb60087c..862a3d1eff60 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -44,6 +44,7 @@
#include <linux/sched/sysctl.h>
#include <linux/memory-tiers.h>
#include <linux/pagewalk.h>
+#include <linux/migrate_offc.h>
#include <asm/tlbflush.h>
@@ -743,6 +744,37 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio)
}
EXPORT_SYMBOL(folio_migrate_flags);
+DEFINE_STATIC_CALL(_folios_copy, folios_mc_copy);
+DEFINE_STATIC_CALL(_can_offc_migrate, can_offc_migrate);
+
+#ifdef CONFIG_OFFC_MIGRATION
+void srcu_mig_cb(struct rcu_head *head)
+{
+ static_call_query(_folios_copy);
+}
+
+void offc_update_migrator(struct migrator *mig)
+{
+ int index;
+
+ mutex_lock(&migrator_mut);
+ index = srcu_read_lock(&mig_srcu);
+ strscpy(migrator.name, mig ? mig->name : "kernel", MIGRATOR_NAME_LEN);
+ static_call_update(_folios_copy, mig ? mig->migrate_offc : folios_mc_copy);
+ static_call_update(_can_offc_migrate, mig ? mig->can_migrate_offc : can_offc_migrate);
+ if (READ_ONCE(migrator.owner))
+ module_put(migrator.owner);
+ xchg(&migrator.owner, mig ? mig->owner : NULL);
+ if (READ_ONCE(migrator.owner))
+ try_module_get(migrator.owner);
+ srcu_read_unlock(&mig_srcu, index);
+ mutex_unlock(&migrator_mut);
+ call_srcu(&mig_srcu, &migrator.srcu_head, srcu_mig_cb);
+ srcu_barrier(&mig_srcu);
+}
+
+#endif /* CONFIG_OFFC_MIGRATION */
+
/************************************************************
* Migration functions
***********************************************************/
@@ -1028,11 +1060,15 @@ static int _move_to_new_folio_prep(struct folio *dst, struct folio *src,
{
int rc = -EAGAIN;
bool is_lru = !__folio_test_movable(src);
+ bool can_migrate;
VM_BUG_ON_FOLIO(!folio_test_locked(src), src);
VM_BUG_ON_FOLIO(!folio_test_locked(dst), dst);
- if (likely(is_lru)) {
+ can_migrate = static_call(_can_offc_migrate)(dst, src);
+ if (unlikely(!can_migrate))
+ rc = -EAGAIN;
+ else if (likely(is_lru)) {
struct address_space *mapping = folio_mapping(src);
if (!mapping)
@@ -1868,7 +1904,10 @@ static void migrate_folios_batch_move(struct list_head *src_folios,
goto out;
/* Batch copy the folios */
- rc = folios_mc_copy(dst_folios, src_folios, nr_batched_folios);
+ rc = static_call(_folios_copy)(dst_folios, src_folios, nr_batched_folios);
+ /* TODO: Is there a better way of handling the poison
+ * recover for batch copy and falling back to serial copy?
+ */
/* TODO: Is there a better way of handling the poison
* recover for batch copy, instead of falling back to serial copy?
diff --git a/mm/migrate_offc.c b/mm/migrate_offc.c
new file mode 100644
index 000000000000..c632928a7c27
--- /dev/null
+++ b/mm/migrate_offc.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/migrate.h>
+#include <linux/migrate_offc.h>
+#include <linux/rculist.h>
+#include <linux/static_call.h>
+
+atomic_t dispatch_to_offc = ATOMIC_INIT(0);
+EXPORT_SYMBOL_GPL(dispatch_to_offc);
+
+DEFINE_MUTEX(migrator_mut);
+DEFINE_SRCU(mig_srcu);
+
+struct migrator migrator = {
+ .name = "kernel",
+ .migrate_offc = folios_mc_copy,
+ .can_migrate_offc = can_offc_migrate,
+ .srcu_head.func = srcu_mig_cb,
+ .owner = NULL,
+};
+
+bool can_offc_migrate(struct folio *dst, struct folio *src)
+{
+ return true;
+}
+EXPORT_SYMBOL_GPL(can_offc_migrate);
+
+void start_offloading(struct migrator *m)
+{
+ int offloading = 0;
+
+ pr_info("starting migration offload by %s\n", m->name);
+ offc_update_migrator(m);
+ atomic_try_cmpxchg(&dispatch_to_offc, &offloading, 1);
+}
+EXPORT_SYMBOL_GPL(start_offloading);
+
+void stop_offloading(void)
+{
+ int offloading = 1;
+
+ pr_info("stopping migration offload by %s\n", migrator.name);
+ offc_update_migrator(NULL);
+ atomic_try_cmpxchg(&dispatch_to_offc, &offloading, 0);
+}
+EXPORT_SYMBOL_GPL(stop_offloading);
+
+unsigned char *get_active_migrator_name(void)
+{
+ return migrator.name;
+}
+EXPORT_SYMBOL_GPL(get_active_migrator_name);
--
2.34.1
