The do_memsw_account() is used to enable or disable legacy memory+swap
accounting in memory cgroup. However with disabled CONFIG_MEMCG_V1, we
don't need to keep checking it. So, let's always return false for
!CONFIG_MEMCG_V1 configs.

Before the patch:

$ size mm/memcontrol.o
   text    data     bss     dec     hex filename
  49928   10736    4172   64836    fd44 mm/memcontrol.o

After the patch:

$ size mm/memcontrol.o
   text    data     bss     dec     hex filename
  49430   10480    4172   64082    fa52 mm/memcontrol.o

Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
---
 mm/memcontrol-v1.h | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h
index 653ff1bad244..6358464bb416 100644
--- a/mm/memcontrol-v1.h
+++ b/mm/memcontrol-v1.h
@@ -22,12 +22,6 @@
 	     iter != NULL;				\
 	     iter = mem_cgroup_iter(NULL, iter, NULL))
 
-/* Whether legacy memory+swap accounting is active */
-static inline bool do_memsw_account(void)
-{
-	return !cgroup_subsys_on_dfl(memory_cgrp_subsys);
-}
-
 unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap);
 
 void drain_all_stock(struct mem_cgroup *root_memcg);
@@ -42,6 +36,12 @@ struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg);
 /* Cgroup v1-specific declarations */
 #ifdef CONFIG_MEMCG_V1
 
+/* Whether legacy memory+swap accounting is active */
+static inline bool do_memsw_account(void)
+{
+	return !cgroup_subsys_on_dfl(memory_cgrp_subsys);
+}
+
 unsigned long memcg_events_local(struct mem_cgroup *memcg, int event);
 unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx);
 unsigned long memcg_page_state_local_output(struct mem_cgroup *memcg, int item);
@@ -94,6 +94,7 @@ extern struct cftype mem_cgroup_legacy_files[];
 
 #else	/* CONFIG_MEMCG_V1 */
 
+static inline bool do_memsw_account(void) { return false; }
 static inline bool memcg1_alloc_events(struct mem_cgroup *memcg) { return true; }
 static inline void memcg1_free_events(struct mem_cgroup *memcg) {}
 
-- 
2.47.1

On Wed 12-03-25 15:25:52, Shakeel Butt wrote:
> The do_memsw_account() is used to enable or disable legacy memory+swap
> accounting in memory cgroup. However with disabled CONFIG_MEMCG_V1, we
> don't need to keep checking it. So, let's always return false for
> !CONFIG_MEMCG_V1 configs.
> 
> Before the patch:
> 
> $ size mm/memcontrol.o
>    text    data     bss     dec     hex filename
>   49928   10736    4172   64836    fd44 mm/memcontrol.o
> 
> After the patch:
> 
> $ size mm/memcontrol.o
>    text    data     bss     dec     hex filename
>   49430   10480    4172   64082    fa52 mm/memcontrol.o
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>

Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!

> ---
>  mm/memcontrol-v1.h | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h
> index 653ff1bad244..6358464bb416 100644
> --- a/mm/memcontrol-v1.h
> +++ b/mm/memcontrol-v1.h
> @@ -22,12 +22,6 @@
>  	     iter != NULL;				\
>  	     iter = mem_cgroup_iter(NULL, iter, NULL))
>  
> -/* Whether legacy memory+swap accounting is active */
> -static inline bool do_memsw_account(void)
> -{
> -	return !cgroup_subsys_on_dfl(memory_cgrp_subsys);
> -}
> -
>  unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap);
>  
>  void drain_all_stock(struct mem_cgroup *root_memcg);
> @@ -42,6 +36,12 @@ struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg);
>  /* Cgroup v1-specific declarations */
>  #ifdef CONFIG_MEMCG_V1
>  
> +/* Whether legacy memory+swap accounting is active */
> +static inline bool do_memsw_account(void)
> +{
> +	return !cgroup_subsys_on_dfl(memory_cgrp_subsys);
> +}
> +
>  unsigned long memcg_events_local(struct mem_cgroup *memcg, int event);
>  unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx);
>  unsigned long memcg_page_state_local_output(struct mem_cgroup *memcg, int item);
> @@ -94,6 +94,7 @@ extern struct cftype mem_cgroup_legacy_files[];
>  
>  #else	/* CONFIG_MEMCG_V1 */
>  
> +static inline bool do_memsw_account(void) { return false; }
>  static inline bool memcg1_alloc_events(struct mem_cgroup *memcg) { return true; }
>  static inline void memcg1_free_events(struct mem_cgroup *memcg) {}
>  
> -- 
> 2.47.1

-- 
Michal Hocko
SUSE Labs

On Wed, Mar 12, 2025 at 03:25:52PM -0700, Shakeel Butt wrote:
> The do_memsw_account() is used to enable or disable legacy memory+swap
> accounting in memory cgroup. However with disabled CONFIG_MEMCG_V1, we
> don't need to keep checking it. So, let's always return false for
> !CONFIG_MEMCG_V1 configs.
> 
> Before the patch:
> 
> $ size mm/memcontrol.o
>    text    data     bss     dec     hex filename
>   49928   10736    4172   64836    fd44 mm/memcontrol.o
> 
> After the patch:
> 
> $ size mm/memcontrol.o
>    text    data     bss     dec     hex filename
>   49430   10480    4172   64082    fa52 mm/memcontrol.o
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>

Nice. It being a jump label avoids the branch, but it's still
unnecessary text and therefor i$ burden on fairly hot paths.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>