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Wed, 29 Oct 2025 21:31:33 +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 bKLiILWHAmkGTwAAD6G6ig (envelope-from ); Wed, 29 Oct 2025 21:31:33 +0000 Message-ID: <937b6cb3-27d5-4416-8152-df12b45979be@suse.cz> Date: Wed, 29 Oct 2025 22:31:33 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 10/19] slab: remove cpu (partial) slabs usage from allocation paths 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: <20251024142927.780367-1-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: <20251024142927.780367-1-clm@meta.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9930A1A000A X-Stat-Signature: 3y8r7ps1fgd4ejbe1ohbxgmm1aw4415d X-Rspam-User: X-HE-Tag: 1761773495-645298 X-HE-Meta: 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 N02SOVmp S9HitCWe2VOhS1PVhRcpgxdQfTGWamz/XnGhn8tRsH63GyNjCrKX7Vz4wRCZuV7knPcxt6hauLHmuMZev7iD42c4LKLabk/mnid2/TzegCu7uLC51wm49uLPbVLwkJdo8zXlyDESms8utFue5iu9C5yTFAO3+4OcVyZ2Tp1wzP/BHLXwXlw9SFR+28lkY6kMqEWbRB4ju6iDUrksDRRD2JjjVHlBgYDP+/QLtdYt7nNQJgaPIOuMT9ugYJnmsYMdjhYf38bgnO1GGZ2NvmGiaHTkDneyGO4F3zk30 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 16:29, Chris Mason wrote: >> else if (!spin_trylock_irqsave(&n->list_lock, flags)) >> return NULL; >> list_for_each_entry_safe(slab, slab2, &n->partial, slab_list) { >> + >> + unsigned long counters; >> + struct slab new; >> + >> if (!pfmemalloc_match(slab, pc->flags)) >> continue; > > Can get_partial_node() return an uninitialized pointer? The variable > 'object' is declared but never initialized. If all slabs in the partial > list fail the pfmemalloc_match() check, the loop completes without > setting 'object', then returns it at the end of the function. > > In the previous version, the equivalent 'partial' variable was explicitly > initialized to NULL. When all slabs were skipped, NULL was returned. Indeed, this can happen. Thanks! >> >> if (IS_ENABLED(CONFIG_SLUB_TINY) || kmem_cache_debug(s)) { >> - void *object = alloc_single_from_partial(s, n, slab, >> + object = alloc_single_from_partial(s, n, slab, >> pc->orig_size); >> - if (object) { >> - partial = slab; >> - pc->object = object; >> + if (object) >> break; >> - } >> continue; >> } >> >> - remove_partial(n, slab); >> - >> - if (!partial) { >> - partial = slab; >> - stat(s, ALLOC_FROM_PARTIAL); >> - >> - if ((slub_get_cpu_partial(s) == 0)) { >> - break; >> - } >> - } else { >> - put_cpu_partial(s, slab, 0); >> - stat(s, CPU_PARTIAL_NODE); >> - >> - if (++partial_slabs > slub_get_cpu_partial(s) / 2) { >> - break; >> - } >> - } >> + /* >> + * get a single object from the slab. This might race against >> + * __slab_free(), which however has to take the list_lock if >> + * it's about to make the slab fully free. >> + */ >> + do { >> + object = slab->freelist; >> + counters = slab->counters; >> + new.freelist = get_freepointer(s, object); >> + new.counters = counters; >> + new.inuse++; >> + } while (!__slab_update_freelist(s, slab, >> + object, counters, >> + new.freelist, new.counters, >> + "get_partial_node")); >> + >> + if (!new.freelist) >> + remove_partial(n, slab); >> } >> spin_unlock_irqrestore(&n->list_lock, flags); >> - return partial; >> + return object; >> } > > [ ... ] > >