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Wed, 29 Oct 2025 15:51:02 +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 hcnzMuY3AmkcBwAAD6G6ig (envelope-from ); Wed, 29 Oct 2025 15:51:02 +0000 Message-ID: <48e0bc5b-ccee-4fce-8a89-a32f79228bb6@suse.cz> Date: Wed, 29 Oct 2025 16:51:02 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 06/19] slab: introduce percpu sheaves bootstrap Content-Language: en-US To: Chris Mason Cc: Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , 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: <20251024152913.1115220-1-clm@meta.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: <20251024152913.1115220-1-clm@meta.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Stat-Signature: 43winrjzi7sgofiq6pr6i3g3gjoz33yo X-Rspam-User: X-Rspamd-Queue-Id: 75D4480004 X-HE-Tag: 1761753064-182308 X-HE-Meta: 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 qXppk4ZX FiNeaVdebpA+6RpsmaFykPKcrAe29/kpJ+3+nz1Zm76xHra7sHdXF6JQr57I21Tv27xjF6RJZHrqCYlIdcey8b8EXpn8jNPbSyyPR6vWsn/pYa+1OZQuj/gE2am7bQzzaiUQ0C7pkwDR7/8F5JVwMeOQnbS1nqC4tOBCdR4DvySSFMM1F5Zpj6ESXTC5BLSo8CgrSUKFJRhwtBpL7TACF2p5CZVCLKrhtNCcFChT3euk1l4D0P+7VUEeA7v3C8v998XLmVWmdfy3rrUh31dSnH4V5VR6ec/QyTgZp 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 10/24/25 17:29, Chris Mason wrote: > On Thu, 23 Oct 2025 15:52:28 +0200 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. >> >> 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 check sheaf_capacity 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. >> > > Hi Vlastimil, > > We're trying out the AI patch review automation on the BPF commits and it had > some questions about a few of these. Since the goal is to actually test the > automation, I'm putting them in unedited, but I did try and make sure they > were valid before sending. > >> diff --git a/mm/slub.c b/mm/slub.c >> index a6e58d3708f4..ecb10ed5acfe 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c > > [ ... ] > >> @@ -7733,8 +7782,7 @@ static void free_kmem_cache_nodes(struct kmem_cache *s) >> void __kmem_cache_release(struct kmem_cache *s) >> { >> cache_random_seq_destroy(s); >> - if (s->cpu_sheaves) >> - pcs_destroy(s); >> + pcs_destroy(s); > > Can pcs_destroy() handle a NULL cpu_sheaves pointer? Looking at the > error path in do_kmem_cache_create(): Good catch! I will leave the condition in __kmem_cache_release(). Thanks!