From: Shakeel Butt <shakeel.butt@linux.dev>
To: Hui Zhu <hui.zhu@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Muchun Song <muchun.song@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Hui Zhu <zhuhui@kylinos.cn>
Subject: Re: [PATCH] mm/memcontrol: hoist pstatc_pcpu assignment out of CPU loop
Date: Thu, 30 Apr 2026 06:03:15 -0700 [thread overview]
Message-ID: <afNS6UJjUl_zQIHS@linux.dev> (raw)
In-Reply-To: <20260429084216.186238-1-hui.zhu@linux.dev>
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>
prev parent reply other threads:[~2026-04-30 13:03 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-29 8:42 [PATCH] mm/memcontrol: hoist pstatc_pcpu assignment out of CPU loop Hui Zhu
2026-04-29 12:26 ` Andrew Morton
2026-04-30 0:45 ` SeongJae Park
2026-04-30 13:03 ` Shakeel Butt [this message]
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