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[109.81.86.48]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4999d078523sm45861335e9.6.2026.08.17.07.10.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Aug 2026 07:10:01 -0700 (PDT) Date: Mon, 17 Aug 2026 16:10:00 +0200 From: Michal Hocko To: Song Hu Cc: akpm@linux-foundation.org, audra@redhat.com, bingfangguo@tencent.com, cgroups@vger.kernel.org, hannes@cmpxchg.org, joshua.hahnjy@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, muchun.song@linux.dev, roman.gushchin@linux.dev, shakeel.butt@linux.dev, zhuhui@kylinos.cn Subject: Re: [PATCH] mm: memcg: flush empty per-cpu stock slots on memcg offlining Message-ID: References: <20260817131221.44761-1-husong@kylinos.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: 76uk9u3krjjwpyfzdj7n3k6f3g4dwrfq X-Rspamd-Queue-Id: 4BA52180002 X-Rspamd-Server: rspam03 X-Rspam-User: X-HE-Tag: 1786975803-829313 X-HE-Meta: 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 K8xobFtm AdZopqsIPT6lYXL8GDnoNuWaNNPlyLBpZocTAOWPyeJy0gIAej61c7vQJImjPfn0DtDyOBvamFTHN7Aw4CMi9nyK67eZZwd/gpj9C6qsTg8U4c2nTX915qxZEKX0YdyFGYGP4KqiDuBQgXpOWhVZtHls8cOUY4dxXmFnjVr2YeDciOqAED9hjI+zPH2S9YLAP9xiYf1Xzq34fPUTwBhSxm/7hfL2FOILqTEYU0DxVxifqxgxp9XXgvs6K6DKrGv4pKDV8Dl7NR/vr8TxqaKSM7qbOfjAc/qAdRELqT03PonmpSjj9vlGhWouE0vOpAjClTJHcu3qiD1JjCqZ9JoC94+cGcJ9u2Up62l9FaB5tWs5lx0x1GjleZnGzIeU2f2MGwn9EJfAsv+pMbL59bgEueDLC4cf3q98NqwAL8GV9XIa7LvkKIp/9hS7z116g0uKGKVzH4+E0Q+057Sk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon 17-08-26 21:58:39, Song Hu wrote: > Hi,Michal > > 在 2026/8/17 21:29, Michal Hocko 写道: > > On Mon 17-08-26 21:12:21, Song Hu wrote: > >> On Mon 17-08-26, Michal Hocko wrote: > >>> Is there any specific reason why the memcg stays in the cache slot > >>> without any pages? > >> > >> consume_stock() doesn't release the slot when nr_pages hits zero. It > >> is kept for the next charge of the same task and only gets displaced > >> by a charge under a different memcg or by CPU hotplug. The problem is > >> that the offlining drain skips empty slots, so the css reference they > >> hold is never dropped unless something unrelated displaces them. > > > > This doesn't answer my question, really, does it? Is there any good > > reason for this implementation? Why do we need to drop references > > remotely when we can do so when the last cached charge is consumed? > > > > Fair enough. There is no strong reason. Keeping the slot > populated after the last page is consumed only saves a > css_get()/css_put() pair when the same memcg charges again on that > CPU - a micro-optimization from the original single-slot > implementation. This would also allow more effective use of the stock because it wouldn't need to throw other stock away when refilling. -- Michal Hocko SUSE Labs