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b=HFwGVGJfkaIy5KBpg96SC/rKobcnOYBnzagj5OPEvKfrKBihzUHUnX6IZ/CEQnC8A GisE6n6TM1ZbJzxzrC+jDcAgerA1xpww1xwWxrFgMbGNquTa0zc5JpP0gvF7fJx3em EeDTV/+QKI4nwYVaU7ZybGyhUKxS9xBc0aCjcYEgSzKjqeg+8u1+/RlYErk2q8Yfgd iSJ+fz15N+R3dhUGHIt9GfU1PABW+e49jYJM3F0lrFS0ePeRSuXgN5aOPUd5SOxOkF fMwm+rH0HnOvRvvZ/CTd/2xbNNd4EX1Pdlu6jDt1Ph7Ms8n79wXywt/BNfYIIbD2m5 ozp8+0YxligEg== From: SeongJae Park To: Hui Zhu Cc: SeongJae Park , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , 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 Date: Wed, 29 Apr 2026 17:45:04 -0700 Message-ID: <20260430004504.113550-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260429084216.186238-1-hui.zhu@linux.dev> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: DD58518000F X-Stat-Signature: f4naz94uui5fbf9uihmubqgexni5gdr4 X-Rspam-User: X-HE-Tag: 1777509913-846567 X-HE-Meta: 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 Hlf2IA+6 Yg5VZ+2ws4/5CWwhg7rjk3VkklY3nJAYXkRPSY+sIP9v+4lTbdLNemPqrhyVo41mTi/8A3rat6g2q4YQDeNbsXrkWVMRLdOl1XkGgJF1a73fHbhvtqbNmeo6pF8ZTYVIzeSMES/RRxXfvhAfAkcZfy/pp6X+cS57Uyaq8vUx1puOTsxfPOqvHXopgemLBW4RGZ61VkHtABVxnRFgh5yX+NjuuxP24bX51WrtaOMckhWCu0TqlxBch8XntxpOxIRkBXOyMd0AMOQim7U+eO7eL1AYdDA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 29 Apr 2026 16:42:16 +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. Makes sense and looks good to me. > > Signed-off-by: Hui Zhu Reviewed-by: SeongJae Park Thanks, SJ [...]