mm: memcg: put cgroup v1-specific code under a config option

Put legacy cgroup v1 memory controller code under a new CONFIG_MEMCG_V1
config option.  The option is turned off by default.  Nobody except those
who are still using cgroup v1 should turn it on.

If the option is not set, memory controller can still be mounted under
cgroup v1, but none of memcg-specific control files are present.

Please note, that not all cgroup v1's memory controller code is guarded
yet (but most of it), it's a subject for some follow-up work.

Thanks to Michal Hocko for providing a better Kconfig option description.

[roman.gushchin@linux.dev: better config option description provided by Michal]
Link: https://lkml.kernel.org/r/ZnxXNtvqllc9CDoo@google.com
Link: https://lkml.kernel.org/r/20240625005906.106920-14-roman.gushchin@linux.dev
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index a70d64ed04f51e87321addf8c37954ce794534c5..796cfa8423461b918a5015b9dc30d70ce000e047 100644 (file)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1851,7 +1851,7 @@ 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);
@@ -1883,7 +1883,7 @@ static inline void mem_cgroup_unlock_pages(void)
        rcu_read_unlock();
 }
 
-#else /* CONFIG_MEMCG */
+#else /* CONFIG_MEMCG_V1 */
 static inline
 unsigned long memcg1_soft_limit_reclaim(pg_data_t *pgdat, int order,
                                        gfp_t gfp_mask,
@@ -1922,6 +1922,6 @@ static inline bool mem_cgroup_oom_synchronize(bool wait)
        return false;
 }
 
-#endif /* CONFIG_MEMCG */
+#endif /* CONFIG_MEMCG_V1 */
 
 #endif /* _LINUX_MEMCONTROL_H */

diff --git a/init/Kconfig b/init/Kconfig
index febdea2afc3be3ffeeb2029386ea931f364dec1c..aca0ae9be04f393ec3f5aea13111954277cfc614 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -969,6 +969,23 @@ config MEMCG
        help
          Provides control over the memory footprint of tasks in a cgroup.
 
+config MEMCG_V1
+       bool "Legacy cgroup v1 memory controller"
+       depends on MEMCG
+       default n
+       help
+         Legacy cgroup v1 memory controller which has been deprecated by
+         cgroup v2 implementation. The v1 is there for legacy applications
+         which haven't migrated to the new cgroup v2 interface yet. If you
+         do not have any such application then you are completely fine leaving
+         this option disabled.
+
+         Please note that feature set of the legacy memory controller is likely
+         going to shrink due to deprecation process. New deployments with v1
+         controller are highly discouraged.
+
+         San N is unsure.
+
 config MEMCG_KMEM
        bool
        depends on MEMCG

diff --git a/mm/Makefile b/mm/Makefile
index 124d4dea20351460f35250e912a53a94dd26c306..d2915f8c9dc0181978e8e263c0dadbeafffa97ff 100644 (file)
--- 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 31522b1c174d58ce8e7c859400bca2ae8c5b0312..72f0e15a939dbc7a0ce3d3b323a9b1e3db25a8d3 100644 (file)
--- a/mm/memcontrol-v1.h
+++ b/mm/memcontrol-v1.h
@@ -70,7 +70,7 @@ 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)
@@ -105,4 +105,23 @@ 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 b47c00f603327760e6d198b6b26b3a8cdebb0afe..53a8491634b9ca563578f70f941a13c355612778 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4398,18 +4398,20 @@ 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,
 };
 
@@ -5581,7 +5583,9 @@ 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