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From: Shakeel Butt To: Hui Zhu Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hui Zhu Subject: Re: [PATCH] mm/memcontrol: hoist pstatc_pcpu assignment out of CPU loop Message-ID: References: <20260429084216.186238-1-hui.zhu@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260429084216.186238-1-hui.zhu@linux.dev> X-Migadu-Flow: FLOW_OUT X-Stat-Signature: e7tjegos5j1ttr9u6a3cg6o3jwpiedtw X-Rspam-User: X-Rspamd-Queue-Id: D83FB40047 X-Rspamd-Server: rspam07 X-HE-Tag: 1777554212-998 X-HE-Meta: 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 5mzsuW6G 0eKyEHcgVTWfFQLOaoXvNR9wWWVOS0yU4REFR5RJMJTPgzJ5I0jI4S/QiSZPmfh2eSfkSpPmDm+0k3xzILjzZo5JsSl7kCfnHPKjfHgW5wi9neaUE/kSdExBxbc4eLSHBteLMOlF7GiY4aPfXPyia5/1OEZIoPn7g5U3qIOYV07nNPECSIr28+qKZ+rN98XYecf6NycrTZxkKlI06lDDhPIKtEpBYuZaIlIlLv+p9yr26vxr+jeMgZlzGWfckwiyhunlP Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 29, 2026 at 04:42:16PM +0800, Hui Zhu wrote: > From: Hui Zhu > > 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 Acked-by: Shakeel Butt