linux-kernel - Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup

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Message-ID: <aTqhm67ouVl8CHQG@tiehlicka>
Date: Thu, 11 Dec 2025 11:48:59 +0100
From: Michal Hocko <mhocko@...e.com>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: hannes@...xchg.org, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
	muchun.song@...ux.dev, akpm@...ux-foundation.org,
	axelrasmussen@...gle.com, yuanchu@...gle.com, weixugc@...gle.com,
	david@...nel.org, zhengqi.arch@...edance.com,
	lorenzo.stoakes@...cle.com, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	lujialin4@...wei.com
Subject: Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

On Thu 11-12-25 01:30:19, Chen Ridong wrote:
> From: Chen Ridong <chenridong@...wei.com>
> 
> The mem_cgroup_size helper is used only in apply_proportional_protection
> to read the current memory usage. Its semantics are unclear and
> inconsistent with other sites, which directly call page_counter_read for
> the same purpose.
> 
> Remove this helper and get its usage via mem_cgroup_protection for
> clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
> to better reflect its meaning.
> 
> No functional changes intended.
> 
> Signed-off-by: Chen Ridong <chenridong@...wei.com>

Yes, this looks much better.
Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

> ---
>  include/linux/memcontrol.h | 18 +++++++-----------
>  mm/memcontrol.c            |  5 -----
>  mm/vmscan.c                |  9 ++++-----
>  3 files changed, 11 insertions(+), 21 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 6a48398a1f4e..603252e3169c 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -557,13 +557,15 @@ static inline bool mem_cgroup_disabled(void)
>  static inline void mem_cgroup_protection(struct mem_cgroup *root,
>  					 struct mem_cgroup *memcg,
>  					 unsigned long *min,
> -					 unsigned long *low)
> +					 unsigned long *low,
> +					 unsigned long *usage)
>  {
> -	*min = *low = 0;
> +	*min = *low = *usage = 0;
>  
>  	if (mem_cgroup_disabled())
>  		return;
>  
> +	*usage = page_counter_read(&memcg->memory);
>  	/*
>  	 * There is no reclaim protection applied to a targeted reclaim.
>  	 * We are special casing this specific case here because
> @@ -919,8 +921,6 @@ static inline void mem_cgroup_handle_over_high(gfp_t gfp_mask)
>  
>  unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg);
>  
> -unsigned long mem_cgroup_size(struct mem_cgroup *memcg);
> -
>  void mem_cgroup_print_oom_context(struct mem_cgroup *memcg,
>  				struct task_struct *p);
>  
> @@ -1102,9 +1102,10 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
>  static inline void mem_cgroup_protection(struct mem_cgroup *root,
>  					 struct mem_cgroup *memcg,
>  					 unsigned long *min,
> -					 unsigned long *low)
> +					 unsigned long *low,
> +					 unsigned long *usage)
>  {
> -	*min = *low = 0;
> +	*min = *low = *usage = 0;
>  }
>  
>  static inline void mem_cgroup_calculate_protection(struct mem_cgroup *root,
> @@ -1328,11 +1329,6 @@ static inline unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
>  	return 0;
>  }
>  
> -static inline unsigned long mem_cgroup_size(struct mem_cgroup *memcg)
> -{
> -	return 0;
> -}
> -
>  static inline void
>  mem_cgroup_print_oom_context(struct mem_cgroup *memcg, struct task_struct *p)
>  {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index dbe7d8f93072..659ce171b1b3 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1621,11 +1621,6 @@ unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
>  	return max;
>  }
>  
> -unsigned long mem_cgroup_size(struct mem_cgroup *memcg)
> -{
> -	return page_counter_read(&memcg->memory);
> -}
> -
>  void __memcg_memory_event(struct mem_cgroup *memcg,
>  			  enum memcg_memory_event event, bool allow_spinning)
>  {
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 670fe9fae5ba..9a6ee80275fc 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2451,9 +2451,9 @@ static inline void calculate_pressure_balance(struct scan_control *sc,
>  static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		struct scan_control *sc, unsigned long scan)
>  {
> -	unsigned long min, low;
> +	unsigned long min, low, usage;
>  
> -	mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low);
> +	mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low, &usage);
>  
>  	if (min || low) {
>  		/*
> @@ -2485,7 +2485,6 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		 * again by how much of the total memory used is under
>  		 * hard protection.
>  		 */
> -		unsigned long cgroup_size = mem_cgroup_size(memcg);
>  		unsigned long protection;
>  
>  		/* memory.low scaling, make sure we retry before OOM */
> @@ -2497,9 +2496,9 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		}
>  
>  		/* Avoid TOCTOU with earlier protection check */
> -		cgroup_size = max(cgroup_size, protection);
> +		usage = max(usage, protection);
>  
> -		scan -= scan * protection / (cgroup_size + 1);
> +		scan -= scan * protection / (usage + 1);
>  
>  		/*
>  		 * Minimally target SWAP_CLUSTER_MAX pages to keep
> -- 
> 2.34.1

-- 
Michal Hocko
SUSE Labs