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Mon, 26 Jan 2026 08:42:50 +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 J4x7Agopd2ltKwAAD6G6ig (envelope-from ); Mon, 26 Jan 2026 08:42:50 +0000 Message-ID: <0c337f99-98b3-4955-b9aa-6a5e9bacb041@suse.cz> Date: Mon, 26 Jan 2026 09:42:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 07/22] slab: introduce percpu sheaves bootstrap Content-Language: en-US To: Hao Li Cc: Harry Yoo , Petr Tesarik , Christoph Lameter , David Rientjes , Roman Gushchin , Andrew Morton , Uladzislau Rezki , "Liam R. Howlett" , Suren Baghdasaryan , Sebastian Andrzej Siewior , Alexei Starovoitov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, bpf@vger.kernel.org, kasan-dev@googlegroups.com References: <20260123-sheaves-for-all-v4-0-041323d506f7@suse.cz> <20260123-sheaves-for-all-v4-7-041323d506f7@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: 417fbsine13mgfiyit6p8j7bafz6urt9 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: B37F51C0002 X-HE-Tag: 1769416972-156121 X-HE-Meta: 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 N4Yp0dtb nIC14pnn9A+tcZzexa+rL0TDn13ixUsChqaM0LaxwZjwkaHbXYRGEtTAglGy1MWr/jSryCpUw76PamJwCdyngYsNPhk6f+mGh7UR0mLNB8iwk6LgDKjQzRmmuda8z1evKRJM45xoudgA64JA8wVwAJX7LFDCVm9TbP6FfauuZcQQ89+oYBK6HshSriqVuoubGQEb4WbYVBPOFFPcDe12B1EJ0rXiaN8eQJkF3TfYvXJceDq4j4VRmVME4USyv1LbRF0XhEZbg682IWK6OQ0PzsCVL2LKadmIWRkIn7GT/F/xg7whMlmZrMeiUaA== 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 1/26/26 07:13, Hao Li wrote: > On Fri, Jan 23, 2026 at 07:52:45AM +0100, Vlastimil Babka wrote: >> Until now, kmem_cache->cpu_sheaves was !NULL only for caches with >> sheaves enabled. Since we want to enable them for almost all caches, >> it's suboptimal to test the pointer in the fast paths, so instead >> allocate it for all caches in do_kmem_cache_create(). Instead of testing >> the cpu_sheaves pointer to recognize caches (yet) without sheaves, test >> kmem_cache->sheaf_capacity for being 0, where needed, using a new >> cache_has_sheaves() helper. >> >> However, for the fast paths sake we also assume that the main sheaf >> always exists (pcs->main is !NULL), and during bootstrap we cannot >> allocate sheaves yet. >> >> Solve this by introducing a single static bootstrap_sheaf that's >> assigned as pcs->main during bootstrap. It has a size of 0, so during >> allocations, the fast path will find it's empty. Since the size of 0 >> matches sheaf_capacity of 0, the freeing fast paths will find it's >> "full". In the slow path handlers, we use cache_has_sheaves() to >> recognize that the cache doesn't (yet) have real sheaves, and fall back. >> Thus sharing the single bootstrap sheaf like this for multiple caches >> and cpus is safe. >> >> Reviewed-by: Harry Yoo >> Signed-off-by: Vlastimil Babka >> --- >> mm/slab.h | 12 ++++++ >> mm/slab_common.c | 2 +- >> mm/slub.c | 123 ++++++++++++++++++++++++++++++++++++------------------- >> 3 files changed, 95 insertions(+), 42 deletions(-) > > Tiny consistency nit: in kfree_rcu_sheaf(), there's a remaining "if > (s->cpu_sheaves)" that could be replaced with "if (cache_has_sheaves(s))" for Ah thanks. > consistency. It's trivial, so no need to respin - happy to have it addressed > opportunistically. Actually we should remove it completely from the fastpath per the design, as __kfree_rcu_sheaf() checks that. Will do. > The rest looks great to me! > > Reviewed-by: Hao Li Thanks!