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Thu, 24 Jul 2025 14:30:49 +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 GrxqHZlDgmhwMwAAD6G6ig (envelope-from ); Thu, 24 Jul 2025 14:30:49 +0000 Message-ID: <9cad7b86-4b77-4881-9cbf-637b6a61695d@suse.cz> Date: Thu, 24 Jul 2025 16:30:49 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 02/14] slab: add sheaf support for batching kfree_rcu() operations Content-Language: en-US To: Uladzislau Rezki Cc: Suren Baghdasaryan , "Liam R. Howlett" , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , linux-mm@kvack.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, maple-tree@lists.infradead.org References: <20250723-slub-percpu-caches-v5-0-b792cd830f5d@suse.cz> <20250723-slub-percpu-caches-v5-2-b792cd830f5d@suse.cz> 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-Stat-Signature: gm1prs91k4a4x1irgnhb9wqi1a4cdmb6 X-Rspamd-Queue-Id: 4F0C6C0014 X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1753367450-220186 X-HE-Meta: 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 ZjpPOhBS ZHIcyxMQz3zfBDXjD2wY7CuiK4BrSjuvb402TDDaJ00N827rRVvLxSUeql1fBhbo0AXhXpRNkfu0kJnlIZS8i0bKoGRPeUplCz6dQRA8FUSA9Yu8gEbo6EvA0K4OpWuOpGHlvCucsGltQTxhvUL8j3aV5oM71hrcgg1RNETy3CnPG4xonA/CpKAAe7vAVk07J1JAfKcRqq4WqyQXqtxaPpG0cGImxiJJa9TNrYJBY1YXBFL8Jm6Es6on/fLSv1jm+qw/tuXNaL9Ydk3wN/HOnhv+ZG+7NfbFJEjbj1q7pZ7e9DJw= 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 7/23/25 18:39, Uladzislau Rezki wrote: > On Wed, Jul 23, 2025 at 03:34:35PM +0200, Vlastimil Babka wrote: >> static bool >> need_offload_krc(struct kfree_rcu_cpu *krcp) >> { >> @@ -1952,6 +1973,9 @@ void kvfree_call_rcu(struct rcu_head *head, void *ptr) >> if (!head) >> might_sleep(); >> >> + if (kfree_rcu_sheaf(ptr)) >> + return; >> + >> > I have a question here. kfree_rcu_sheaf(ptr) tries to revert freeing > an object over one more newly introduced path. This patch adds infra > for such purpose whereas we already have a main path over which we > free memory. > > Why do not we use existing logic? As i see you can do: > > if (unlikely(!slab_free_hook(s, p[i], init, true))) { > p[i] = p[--sheaf->size]; > continue; > } > > in the kfree_rcu_work() function where we process all ready to free objects. I'm not sure I understand. In kfree_rcu_work() we process individual objects. There is no sheaf that you reference in the code above? Or are you suggesting we add e.g. a "channel" of sheaves to process in addition to the existing channels of objects? > I mean, for slab objects we can replace kfree_bulk() and scan all pointers > and free them over slab_free_hook(). The desired outcome after __rcu_free_sheaf_prepare() is to take the whole sheaf and have it reused, not free individual objects. So we call slab_free_hook() in __rcu_free_sheaf_prepare() but don't actually free individual objects as necessary. > Also we do use a pooled API and other improvements to speed up freeing. It could be useful to know the details as in Suren's measurements there's issues with kfree_rcu() using sheaves when lazy rcu is used. Is the kfree_rcu() infra avoiding being too lazy somehow? We could use the same techniques for sheaves. > Thanks! > > -- > Uladzislau Rezki