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Thu, 12 Feb 2026 11:52:46 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id 9+vXNA6/jWlXcwAAD6G6ig (envelope-from ); Thu, 12 Feb 2026 11:52:46 +0000 Message-ID: <3b9be1ce-ef00-481e-b36d-5b843be55d10@suse.cz> Date: Thu, 12 Feb 2026 12:52:46 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/7] mm/slab: introduce k[v]free_rcu() with struct rcu_ptr Content-Language: en-US To: Uladzislau Rezki , Harry Yoo Cc: Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Johannes Weiner , Shakeel Butt , Michal Hocko , Hao Li , Alexei Starovoitov , Puranjay Mohan , Andrii Nakryiko , Amery Hung , Catalin Marinas , "Paul E . McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Dave Chinner , Qi Zheng , Muchun Song , rcu@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org References: <20260206093410.160622-1-harry.yoo@oracle.com> <20260206093410.160622-2-harry.yoo@oracle.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: C54F81A0002 X-Stat-Signature: j6qfgq349bfmr6qgnqzztzi7kkha3yk8 X-Rspam-User: X-HE-Tag: 1770897168-845216 X-HE-Meta: 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 35guhUIj b2CPXWl4WlrMfLc87RuxQTaSvrBfPYNlmclHV578NsUgJXrOJLtqG8Mxx5DhN0VXuqa62H2P+dYMTcEMatGXIta3naW27vEHxjvbsbHaNvCLTPjP5keoJEB4daoLGSYvj6z6lIDRLY31v86b7C/UMOXJzTlv1FdYD1qwFsPkzTR0QMqkEwK+AGMlR5s00kYlIcQgwjCw/boAOAw/+yfcGJj4O4btVWjEuxRQs/1o2MbPGstd2yRxmwzVz6AXaS6e2M10QQlaMWsovJ0y/f0vQ84wkbYxbwe/+OuraftyFyIeEM2L+kbBz7mmTCDVd3dhii4Fn7YwX5XGUjoD2MlCBPYt21rsNpc5WZhFVKkDIqjR7eW1i0Mtssm5sRaTU/nKWzHhQNDr1bwGPr64SnnuCV2lejQ== 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 2/11/26 11:16, Uladzislau Rezki wrote: > On Fri, Feb 06, 2026 at 06:34:04PM +0900, Harry Yoo wrote: >> k[v]free_rcu() repurposes two fields of struct rcu_head: 'func' to store >> the start address of the object, and 'next' to link objects. >> >> However, using 'func' to store the start address is unnecessary: >> >> 1. slab can get the start address from the address of struct rcu_head >> field via nearest_obj(), and >> >> 2. vmalloc and large kmalloc can get the start address by aligning >> down the address of the struct rcu_head field to the page boundary. >> >> Therefore, allow an 8-byte (on 64-bit) field (of a new type called >> struct rcu_ptr) to be used with k[v]free_rcu() with two arguments. >> >> Some users use both call_rcu() and k[v]free_rcu() to process callbacks >> (e.g., maple tree), so it makes sense to have struct rcu_head field >> to handle both cases. However, many users that simply free objects via >> kvfree_rcu() can save one pointer by using struct rcu_ptr instead of >> struct rcu_head. >> >> Note that struct rcu_ptr is a single pointer only when >> CONFIG_KVFREE_RCU_BATCHED=y. To keep kvfree_rcu() implementation minimal >> when CONFIG_KVFREE_RCU_BATCHED is disabled, struct rcu_ptr is the size >> as struct rcu_head, and the implementation of kvfree_rcu() remains >> unchanged in that configuration. Won't that be too limiting, if we can't shrink structures (e.g. BPF) unconditionally? Or acceptable because CONFIG_KVFREE_RCU_BATCHED=n is uncommon?