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Mon, 19 Jan 2026 09:13:51 +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 OFZ/Fs/1bWnsQwAAD6G6ig (envelope-from ); Mon, 19 Jan 2026 09:13:51 +0000 Message-ID: <41048e09-5dd9-42a6-b5d8-dadee3ecfd9c@suse.cz> Date: Mon, 19 Jan 2026 10:13:51 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 06/21] slab: introduce percpu sheaves bootstrap Content-Language: en-US To: Harry Yoo , Suren Baghdasaryan Cc: Petr Tesarik , Christoph Lameter , David Rientjes , Roman Gushchin , Hao Li , Andrew Morton , Uladzislau Rezki , "Liam R. Howlett" , 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: <20260116-sheaves-for-all-v3-0-5595cb000772@suse.cz> <20260116-sheaves-for-all-v3-6-5595cb000772@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: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 7BD2A14000B X-Stat-Signature: kgduy3ca85e3zzd45kbqqjn7qzgw9a98 X-Rspam-User: X-HE-Tag: 1768814033-783891 X-HE-Meta: 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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 1/19/26 04:40, Harry Yoo wrote: > On Sat, Jan 17, 2026 at 02:11:02AM +0000, Suren Baghdasaryan wrote: >> On Fri, Jan 16, 2026 at 2:40 PM 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. >> >> I don't think kmem_cache_prefill_sheaf() handles this case, does it? >> Or do you rely on the caller to never try prefilling a bootstrapped >> sheaf? > > If a cache doesn't have sheaves, s->sheaf_capacity should be 0, > so the sheaf returned by kmem_cache_prefill_sheaf() should be > "oversized" one... unless the user tries to prefill a sheaf with > size == 0? I'll add a if (unlikely(!size)) return NULL; to kmem_cache_prefill_sheaf() so we don't have to deal with oversized sheaves of size 0 just for this theoretical case...