Re: [PATCH] mm/memcontrol: hoist pstatc_pcpu assignment out of CPU loop

Shakeel Butt
2026-04-30T13:03:32Z

On Wed, Apr 29, 2026 at 04:42:16PM +0800, Hui Zhu wrote:
> From: Hui Zhu <zhuhui@kylinos.cn>
>
> In mem_cgroup_alloc(), the assignment of pstatc_pcpu is invariant
> with respect to the for_each_possible_cpu() loop: both the 'parent'
> pointer and 'parent->vmstats_percpu' remain constant throughout all
> iterations.
>
> The original code redundantly re-evaluated the 'if (parent)'
> condition and reassigned pstatc_pcpu on every CPU iteration, then
> repeated the same ternary check 'parent ? pstatc_pcpu : NULL' when
> storing into statc->parent_pcpu.
>
> Move the single conditional assignment of pstatc_pcpu to before the
> loop, resolving both the loop-invariant placement issue and the
> duplicated null check. On systems with a large number of possible
> CPUs, this eliminates repeated branch evaluation with no functional
> change.
>
> No functional change intended.
>
> Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>