Re: [PATCH v2 1/2] memcg: move mem_cgroup_swappiness and vm_swappiness to mm/swap.h

[Tao Cui]

Reviewed-by: Song Hu <husong@xxxxxxxxxx>
在 2026/7/16 11:17, Ridong 写道:
> From: Ridong Chen <chenridong@xxxxxxxxxx>
> 
> The per-memcg swappiness knob is v1-only; v2 always uses global
> vm_swappiness and ignores the per-cgroup field.
> 
> Both mem_cgroup_swappiness() and vm_swappiness are only used within
> mm/ (memcontrol.c, memcontrol-v1.c, vmscan.c), so move them out of the
> public include/linux/swap.h into the mm-private mm/swap.h. This keeps
> unrelated declarations out of include/linux/swap.h.
> 
> Guard memcg->swappiness with CONFIG_MEMCG_V1 as well, so v2-only
> kernels drop the unused field.
> 
> No functional change for v1; v2-only kernels drop the unused field.
> 
> Signed-off-by: Ridong Chen <chenridong@xxxxxxxxxx>
> ---
>  include/linux/memcontrol.h |  4 ++--
>  include/linux/swap.h       | 19 -------------------
>  mm/memcontrol.c            |  4 ++--
>  mm/swap.h                  | 20 ++++++++++++++++++++
>  4 files changed, 24 insertions(+), 23 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 957260677678..e7a794dfb40e 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -239,8 +239,6 @@ struct mem_cgroup {
>  	 */
>  	bool oom_group;
>  
> -	int swappiness;
> -
>  	/* memory.events and memory.events.local */
>  	struct cgroup_file events_file;
>  	struct cgroup_file events_local_file;
> @@ -318,6 +316,8 @@ struct mem_cgroup {
>  	/* List of events which userspace want to receive */
>  	struct list_head event_list;
>  	spinlock_t event_list_lock;
> +
> +	int swappiness;
>  #endif /* CONFIG_MEMCG_V1 */
>  
>  	struct mem_cgroup_per_node *nodeinfo[];
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 696ed01709c2..330a420fd6de 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -309,7 +309,6 @@ static inline bool lru_cache_disabled(void)
>  }
>  
>  extern unsigned long shrink_all_memory(unsigned long nr_pages);
> -extern int vm_swappiness;
>  long remove_mapping(struct address_space *mapping, struct folio *folio);
>  
>  #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
> @@ -468,25 +467,7 @@ static inline int add_swap_extent(struct swap_info_struct *sis,
>  }
>  #endif /* CONFIG_SWAP */
>  #ifdef CONFIG_MEMCG
> -static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
> -{
> -	/* Cgroup2 doesn't have per-cgroup swappiness */
> -	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
> -		return READ_ONCE(vm_swappiness);
> -
> -	/* root ? */
> -	if (mem_cgroup_disabled() || mem_cgroup_is_root(memcg))
> -		return READ_ONCE(vm_swappiness);
> -
> -	return READ_ONCE(memcg->swappiness);
> -}
> -
>  void lru_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent, int nid);
> -#else
> -static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
> -{
> -	return READ_ONCE(vm_swappiness);
> -}
>  #endif
>  
>  #if defined(CONFIG_SWAP) && defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 22f55aeb94f3..d6ba276740ea 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -63,6 +63,7 @@
>  #include <linux/sched/isolation.h>
>  #include <linux/kmemleak.h>
>  #include "internal.h"
> +#include "swap.h"
>  #include "swap_table.h"
>  #include <net/sock.h>
>  #include <net/ip.h>
> @@ -4174,11 +4175,10 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
>  #endif
>  	page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX);
>  	if (parent) {
> -		WRITE_ONCE(memcg->swappiness, mem_cgroup_swappiness(parent));
> -
>  		page_counter_init(&memcg->memory, &parent->memory, memcg_on_dfl);
>  		page_counter_init(&memcg->swap, &parent->swap, false);
>  #ifdef CONFIG_MEMCG_V1
> +		WRITE_ONCE(memcg->swappiness, mem_cgroup_swappiness(parent));
>  		memcg->memory.track_failcnt = !memcg_on_dfl;
>  		WRITE_ONCE(memcg->oom_kill_disable, READ_ONCE(parent->oom_kill_disable));
>  		page_counter_init(&memcg->kmem, &parent->kmem, false);
> diff --git a/mm/swap.h b/mm/swap.h
> index b51ad3071a73..a0e04b97a466 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
> @@ -4,6 +4,7 @@
>  
>  #include <linux/atomic.h> /* for atomic_long_t */
>  #include <linux/mm.h> /* for PAGE_SHIFT */
> +#include <linux/memcontrol.h> /* for mem_cgroup_swappiness() */
>  struct mempolicy;
>  struct swap_iocb;
>  struct swap_memcg_table;
> @@ -76,6 +77,25 @@ enum swap_cluster_flags {
>  	CLUSTER_FLAG_MAX,
>  };
>  
> +extern int vm_swappiness;
> +
> +static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
> +{
> +#ifdef CONFIG_MEMCG_V1
> +	/* Cgroup2 doesn't have per-cgroup swappiness */
> +	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
> +		return READ_ONCE(vm_swappiness);
> +
> +	/* root ? */
> +	if (mem_cgroup_disabled() || mem_cgroup_is_root(memcg))
> +		return READ_ONCE(vm_swappiness);
> +
> +	return READ_ONCE(memcg->swappiness);
> +#else
> +	return READ_ONCE(vm_swappiness);
> +#endif
> +}
> +
>  #ifdef CONFIG_SWAP
>  #include <linux/swapops.h> /* for swp_offset */
>  #include <linux/blk_types.h> /* for bio_end_io_t */