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Sat, 19 Sep 2026 02:56:34 +0000 X-Mizu-Trace-ID: 1f3e88304aab8456 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.700.51.1.1\)) Subject: Re: [PATCH 2/4] memcg: base swap charge accounting on memcgid root status From: Muchun Song In-Reply-To: <20260918-bingfangguo-memcgid-rework-v1-2-5bbf3220d88f@tencent.com> Date: Sat, 19 Sep 2026 10:56:15 +0800 Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Andrew Morton , Dave Chinner , Qi Zheng , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , David Hildenbrand , Lorenzo Stoakes , Bingfang Guo , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20260918-bingfangguo-memcgid-rework-v1-0-5bbf3220d88f@tencent.com> <20260918-bingfangguo-memcgid-rework-v1-2-5bbf3220d88f@tencent.com> To: bingfangguo@tencent.com X-Mailer: Apple Mail (2.3864.700.51.1.1) X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 896F120002 X-Rspam-User: X-Stat-Signature: dqtfs5moeiykixfnxquaiod4y7apx16d X-HE-Tag: 1789786595-561925 X-HE-Meta: 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 RngHL3QR YExXVwEHD298OhQKC1U36IZXHFjxbu2389dhskXLhIfJLaXIpmY+I7wXzglkuyi4hOg6Rn2uTF1Og5BMr3S01VD1xYFIXVDQS4uJ0sJ2sopcNyfFPIjiX6RVrAEdj1ljCqWuUGgwqf0EmP0tB9wPJDGWJG35UcoZUxn/ZWlxhY60QYOVzR+FjdHscP4Z2dJ6sz5D5q8+xcERQ6stozITznex0ZqhpoH45L6RH+ifxOf3KAIs297kqxtwo22xtflruXP/iuIyKRV9ApYl4fsl9e2EOMAQEdRVw+9Gdvbnsv0FWkscvhFANDwqcnQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Sep 18, 2026, at 17:18, Bingfang Guo via B4 Relay = wrote: >=20 > From: Bingfang Guo >=20 > A private ID currently pins its original memcg, so testing whether the > ID belongs to root is equivalent to testing whether the resolved memcg > is root. >=20 > That equivalence will no longer hold when IDs refer to objcgs. A > non-root ID may resolve to root after reparenting, but its swap = entries > still carry counter charges inherited by root. Skipping their uncharge > based on the resolved memcg would leave those charges behind. >=20 > Use the private ID's root status to decide whether a swap entry = carries > a counter charge. A root-ID entry carries none, while a non-root-ID > entry must release its charge even if its current accounting memcg has > become root. >=20 > This patch adds a new helper to check if the memcgid equals to that of > the root memcg. For swap uncharging and v2 swap charging, simply = decide > whether to charge/uncharge memsw or swap counter based on the swap > memcgid is root or not. For v1 swapout, don't recharge the memsw > counter, just cancel the charge if the swap memcg ID refers to the = root > memcg. >=20 > This makes memory and swap charging have similar semantics: one relys = on > the objcg's root status, and the other relys on the memcgid's root > status. >=20 > Signed-off-by: Bingfang Guo Acked-by: Muchun Song