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

SeongJae Park
2026-04-30T00:45:12Z

On Wed, 29 Apr 2026 16:42:16 +0800 Hui Zhu <hui.zhu@linux.dev> 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.

Makes sense and looks good to me.

>
> Signed-off-by: Hui Zhu <zhuhui@kylinos.cn>

Reviewed-by: SeongJae Park <sj@kernel.org>

Thanks,
SJ …