Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

[Michal Koutný]

Hi Ridong.

On Thu, Dec 11, 2025 at 01:30:19AM +0000, Chen Ridong <chenridong@xxxxxxxxxxxxxxx> wrote:
> From: Chen Ridong <chenridong@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>

Why does mem_cgroup_calculate_protection "calculate" usage for its
callers? Couldn't you just the change source in
apply_proportional_protection()?

Thanks,
Michal

> @@ -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 cgroup_size = page_counter_read(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

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