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AJvYcCVRI3x8g/zAEkegnb6/kA4vcX/qf37+mPTJVcQT7h4xKIvx/Rwqe89o5Kw0VoCBmk3SCoH+THSx8w==@kvack.org X-Gm-Message-State: AOJu0YyOA6cKnEgbxwd5yrqYrMaWIeH7p/XWpDvRxzbzitRCcJUNhcX5 3AOXktu+vn/RIypStd7eMCLlhybs6B9E7urm/VyVLZzU7GhKe2P3mWSKQJVMcAiAi4Dqm5lv1XL 7vYr/1Ri6Bs7JH7YsRw== X-Received: from wmpx37.prod.google.com ([2002:a05:600c:18a5:b0:476:ddb0:2391]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:458d:b0:47f:f952:d207 with SMTP id 5b1f17b1804b1-4801e341e2emr60365675e9.19.1768650907837; Sat, 17 Jan 2026 03:55:07 -0800 (PST) Date: Sat, 17 Jan 2026 11:55:06 +0000 In-Reply-To: Mime-Version: 1.0 References: <20260116-rcu-box-v1-0-38ebfbcd53f0@google.com> Message-ID: Subject: Re: [PATCH RFC 0/2] rcu box container for Rust + maple tree load_rcu From: Alice Ryhl To: Boqun Feng Cc: "Paul E. McKenney" , "Liam R. Howlett" , Gary Guo , Miguel Ojeda , "=?utf-8?B?QmrDtnJu?= Roy Baron" , Benno Lossin , Andreas Hindborg , Trevor Gross , Danilo Krummrich , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Andrew Ballance , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, rcu@vger.kernel.org, maple-tree@lists.infradead.org, linux-mm@kvack.org Content-Type: text/plain; charset="utf-8" X-Stat-Signature: khztwm1nsway38rs717h39mhd31t13n7 X-Rspamd-Queue-Id: 6D6A7C0002 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1768650909-833881 X-HE-Meta: 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 DJVZOQ9A 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Jan 17, 2026 at 08:06:40AM +0800, Boqun Feng wrote: > On Fri, Jan 16, 2026 at 03:46:35PM +0000, Alice Ryhl wrote: > > I'm sending this RFC to share an experiment I'm looking at. This may let > > us replace the range allocator in Rust Binder with a maple tree. > > > > Thank you, Alice. > > > An RcuBox is like a Box except that it lets you obtain a &T that > > outlives the box by a grace period. It does not allow mutable access to > > I think the `RcuBox` can be folded into the more generic RCU pointer api > [1], e.g. Rcu>> where RcuBoxInner: HasRcuHead. The > benefits are at least 1) we use relaxed atomic read for RCU readers > which guarantees address dependency that RCU needs under LKMM (while in > the RcuBox here, we just use plain reads), 2) we also support mutable > access as well. 1) But mtree_load() does use rcu_dereference() to obtain the pointer? 1) "relaxed atomic" does not sound like something that provides an address dependency to me. 2) How do you intend to provide mutable access? By waiting a grace period? > As for the progress of that effort, the Rcu atomic pointer is almost > ready [2], I will likely send it early next week. For the `HasRcuHead` > part, as you may be aware, I'm working on a generic `HasField` approach > to avoid duplication of `Has*` trait and macros [3], that requires some > syn adjustments from Gary and Benno, but they should be available next > cycle. I will probably send the patches for reviews before that. Once we > have that `HasRcuHead` should be easily to add. > > Given the WIP code I have, I *think* we are not that far from providing > what you need for binder. Hmm, so I looked over [2], and I think my RcuBox is an RcuOld<_> rather than an Rcu<_> under this model. Though I can't afford to pay synchronize_rcu() for cleanup - I need kfree_rcu(). Alice