[PATCH v1 13/14] mm: memcg: put cgroup v1-related members of task_struct under config option

[Roman Gushchin <roman.gushchin@linux.dev>]

Guard cgroup v1-related members of task_struct under the CONFIG_MEMCG_V1
config option, so that users who adopted cgroup v2 don't have to waste
the memory for fields which are never accessed.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
 include/linux/memcontrol.h |  2 +-
 init/Kconfig               |  9 +++++++++
 mm/Makefile                |  3 ++-
 mm/memcontrol-v1.h         | 21 ++++++++++++++++++++-
 mm/memcontrol.c            | 10 +++++++---
 5 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 7474b20a5d3f5..aaa97ec0634f7 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1845,7 +1845,7 @@ static inline bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg)
 
 /* Cgroup v1-related declarations */
 
-#ifdef CONFIG_MEMCG
+#ifdef CONFIG_MEMCG_V1
 unsigned long memcg1_soft_limit_reclaim(pg_data_t *pgdat, int order,
 					gfp_t gfp_mask,
 					unsigned long *total_scanned);
diff --git a/init/Kconfig b/init/Kconfig
index febdea2afc3be..5191b6435b4e7 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -969,6 +969,15 @@ config MEMCG
 	help
 	  Provides control over the memory footprint of tasks in a cgroup.
 
+config MEMCG_V1
+	bool "Legacy memory controller"
+	depends on MEMCG
+	default n
+	help
+	  Legacy cgroup v1 memory controller.
+
+	  San N is unsure.
+
 config MEMCG_KMEM
 	bool
 	depends on MEMCG
diff --git a/mm/Makefile b/mm/Makefile
index 124d4dea20351..d2915f8c9dc01 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -96,7 +96,8 @@ obj-$(CONFIG_NUMA) += memory-tiers.o
 obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o
 obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o
 obj-$(CONFIG_PAGE_COUNTER) += page_counter.o
-obj-$(CONFIG_MEMCG) += memcontrol.o memcontrol-v1.o vmpressure.o
+obj-$(CONFIG_MEMCG_V1) += memcontrol-v1.o
+obj-$(CONFIG_MEMCG) += memcontrol.o vmpressure.o
 ifdef CONFIG_SWAP
 obj-$(CONFIG_MEMCG) += swap_cgroup.o
 endif
diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h
index 89d4207930481..64b053d7f131e 100644
--- a/mm/memcontrol-v1.h
+++ b/mm/memcontrol-v1.h
@@ -75,7 +75,7 @@ unsigned long memcg_page_state_local_output(struct mem_cgroup *memcg, int item);
 int memory_stat_show(struct seq_file *m, void *v);
 
 /* Cgroup v1-specific declarations */
-
+#ifdef CONFIG_MEMCG_V1
 void memcg1_remove_from_trees(struct mem_cgroup *memcg);
 
 static inline void memcg1_soft_limit_reset(struct mem_cgroup *memcg)
@@ -110,4 +110,23 @@ void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s);
 extern struct cftype memsw_files[];
 extern struct cftype mem_cgroup_legacy_files[];
 
+#else	/* CONFIG_MEMCG_V1 */
+
+static inline void memcg1_remove_from_trees(struct mem_cgroup *memcg) {}
+static inline void memcg1_soft_limit_reset(struct mem_cgroup *memcg) {}
+static inline bool memcg1_wait_acct_move(struct mem_cgroup *memcg) { return false; }
+static inline void memcg1_css_offline(struct mem_cgroup *memcg) {}
+
+static inline bool memcg1_oom_prepare(struct mem_cgroup *memcg, bool *locked) { return true; }
+static inline void memcg1_oom_finish(struct mem_cgroup *memcg, bool locked) {}
+static inline void memcg1_oom_recover(struct mem_cgroup *memcg) {}
+
+static inline void memcg1_check_events(struct mem_cgroup *memcg, int nid) {}
+
+static inline void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s) {}
+
+extern struct cftype memsw_files[];
+extern struct cftype mem_cgroup_legacy_files[];
+#endif	/* CONFIG_MEMCG_V1 */
+
 #endif	/* __MM_MEMCONTROL_V1_H */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 8a28ba4ca93ea..8cbceeb9c7ac4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4473,18 +4473,20 @@ struct cgroup_subsys memory_cgrp_subsys = {
 	.css_free = mem_cgroup_css_free,
 	.css_reset = mem_cgroup_css_reset,
 	.css_rstat_flush = mem_cgroup_css_rstat_flush,
-	.can_attach = memcg1_can_attach,
 #if defined(CONFIG_LRU_GEN) || defined(CONFIG_MEMCG_KMEM)
 	.attach = mem_cgroup_attach,
 #endif
-	.cancel_attach = memcg1_cancel_attach,
-	.post_attach = memcg1_move_task,
 #ifdef CONFIG_MEMCG_KMEM
 	.fork = mem_cgroup_fork,
 	.exit = mem_cgroup_exit,
 #endif
 	.dfl_cftypes = memory_files,
+#ifdef CONFIG_MEMCG_V1
+	.can_attach = memcg1_can_attach,
+	.cancel_attach = memcg1_cancel_attach,
+	.post_attach = memcg1_move_task,
 	.legacy_cftypes = mem_cgroup_legacy_files,
+#endif
 	.early_init = 0,
 };
 
@@ -5655,7 +5657,9 @@ static int __init mem_cgroup_swap_init(void)
 		return 0;
 
 	WARN_ON(cgroup_add_dfl_cftypes(&memory_cgrp_subsys, swap_files));
+#ifdef CONFIG_MEMCG_V1
 	WARN_ON(cgroup_add_legacy_cftypes(&memory_cgrp_subsys, memsw_files));
+#endif
 #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
 	WARN_ON(cgroup_add_dfl_cftypes(&memory_cgrp_subsys, zswap_files));
 #endif
-- 
2.45.1