linux-kernel - Re: [PATCH -next v2 2/2] memcg: remove mem_cgroup

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Message-ID: <aTkp1tIIiw8Nti10@tiehlicka>
Date: Wed, 10 Dec 2025 09:05:42 +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 v2 2/2] memcg: remove mem_cgroup_size()

On Wed 10-12-25 07:11:42, 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 replace its usage with page_counter_read for
> clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
> to better reflect its meaning.
> 
> This change is safe because page_counter_read() is only called when memcg
> is enabled in the apply_proportional_protection.
> 
> No functional changes intended.

I would prefer to keep the code as is. 

Btw.
[...]
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 670fe9fae5ba..fe48d0376e7c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2451,6 +2451,7 @@ 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)
>  {
> +#ifdef CONFIG_MEMCG
>  	unsigned long min, low;
>  
>  	mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low);
[...]
> @@ -2508,6 +2509,7 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		 */
>  		scan = max(scan, SWAP_CLUSTER_MAX);
>  	}
> +#endif
>  	return scan;
>  }

This returns a random garbage for !CONFIG_MEMCG, doesn't it?

-- 
Michal Hocko
SUSE Labs