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Fri, 16 Jan 2026 11:01:23 +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 EV4uIYMaamnwGQAAD6G6ig (envelope-from ); Fri, 16 Jan 2026 11:01:23 +0000 Message-ID: Date: Fri, 16 Jan 2026 12:01:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v2 03/20] mm/slab: make caches with sheaves mergeable Content-Language: en-US To: Harry Yoo Cc: Suren Baghdasaryan , 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: <20260112-sheaves-for-all-v2-0-98225cfb50cf@suse.cz> <20260112-sheaves-for-all-v2-3-98225cfb50cf@suse.cz> <4e73da60-b58d-40bd-86ed-a0243967017b@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: rspam12 X-Rspamd-Queue-Id: 6EBC84001A X-Stat-Signature: h1zu4zf57xh543ysicps6dj3dk1rzg9e X-Rspam-User: X-HE-Tag: 1768561286-884212 X-HE-Meta: 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 wfaflkkv reaL7HGuWrKnF2KTJ+ygI5K6MkQuxJmu0VvcB44r058SZR6lUP1btLmZqeg/pT5ZKL1G5FLTqtw7oVU06xyX7oPRc9owB0WPl0CVAY71kYUHPYRbzqGvjymvhqAYuNpCiqrNceBHt0ip0XQcgjIEHar6YmMj5PeBug5uCZ3FwgiZn94X7QKRT4bEhErzkE0iGtomvJjHnJy3I+FrAIm/nh8PXUPMd/E0YRS/zOrAdJsXd6mWx33Xrm2DxKTuhllXIjxeb+lUbMAFAqVI2pLNk10m7Q4klFqIseCjRCTy/v6fYIXScJH8MRBJNUw== 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 1/16/26 09:46, Harry Yoo wrote: > On Fri, Jan 16, 2026 at 08:24:02AM +0100, Vlastimil Babka wrote: >> On 1/16/26 01:22, Suren Baghdasaryan wrote: >> > On Mon, Jan 12, 2026 at 3:17 PM Vlastimil Babka wrote: >> >> @@ -337,6 +331,13 @@ struct kmem_cache *__kmem_cache_create_args(const char *name, >> >> flags &= ~SLAB_DEBUG_FLAGS; >> >> #endif >> >> >> >> + /* >> >> + * Caches with specific capacity are special enough. It's simpler to >> >> + * make them unmergeable. >> >> + */ >> >> + if (args->sheaf_capacity) >> >> + flags |= SLAB_NO_MERGE; >> > >> > So, this is very subtle and maybe not that important but the comment >> > for kmem_cache_args.sheaf_capacity claims "When slub_debug is enabled >> > for the cache, the sheaf_capacity argument is ignored.". With this >> > change this argument is not completely ignored anymore... It sets >> > SLAB_NO_MERGE even if slub_debug is enabled, doesn't it? >> >> True, but the various debug flags set by slub_debug also prevent merging so >> it doesn't change the outcome. > > nit: except for slub_debug=F (SLAB_CONSISTENCY_CHECKS), since it doesn't > prevent merging (it's in SLAB_DEBUG_FLAGS but not in SLAB_NEVER_MERGE). Hm right. But I think that's wrong then and it should be there. SLAB_CONSISTENCY_CHECKS is enough to stop using the fastpaths (both before/after sheaves) so it should be a reason not to merge.