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Fri, 18 Sep 2026 12:08:21 +0000 X-Mizu-Trace-ID: ac9122ca51626832 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 1/4] memcg: keep swap charging under RCU protection From: Muchun Song In-Reply-To: <20260918-bingfangguo-memcgid-rework-v1-1-5bbf3220d88f@tencent.com> Date: Fri, 18 Sep 2026 20:07:59 +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-v1-1-5bbf3220d88f@tencent.com> To: bingfangguo@tencent.com X-Mailer: Apple Mail (2.3864.700.51.1.1) X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: k5nzyq4b1ma4bb6rfo73t4p7brp9oeb6 X-Rspamd-Queue-Id: DEF0440004 X-HE-Tag: 1789733302-283635 X-HE-Meta: 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 +AgRLVUS wqZHacE616Ll3/uXIEs4wphtkmQ/xIUwmBifZKjnf90tgG3FDBQez7kPllMNga2n8IloYOQNtOsNdDZ5wJm/iHgSKH9+HesSsqHJb9mnYOJeIEq8xjJtztWdp0L3wNKMSHbKsshZVLLWeDLnw+BqiSBoOYp/IFKqIAcx6i671xcVl127y9/eJvn184qGIBpanMWmyn/+5ZdNNGlKejV14/qVP12BrKN07eGQjRARCIC0pdudAm/KDGcbiyfYTNzPEtRmV3J9S75HuLEjCOZyO4KauTgyheSKakSYIh8tsb/vITruLuAyCmjIZcw== 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 > This is a preparatory work for unbinding memcgid from memcg. No > functional change. >=20 > The swap charging path currently drops its RCU read lock after = acquiring > a private ID reference. This is safe because the ID reference pins the > memcg's CSS. >=20 > Moving private ID references to objcgs will remove that lifetime > guarantee. Keep the RCU read lock held while accessing the memcg for > counter charging, statistics and failure handling. (This matches what > __memcg1_swapout() already does.). >=20 > Save the private ID before dropping the RCU read lock, and use the = saved > value when recording the swap entry. The swap cluster locking remains > outside the RCU read-side critical section. >=20 > Signed-off-by: Bingfang Guo Acked-by: Muchun Song Thanks.