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Tue, 27 Jan 2026 17:06:12 +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 qiBrDITweGlTXQAAD6G6ig (envelope-from ); Tue, 27 Jan 2026 17:06:12 +0000 Message-ID: <0409661a-4612-48e8-b394-ec21b744d17f@suse.cz> Date: Tue, 27 Jan 2026 18:06:11 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V1 0/2] Only allow SLAB_OBJ_EXT_IN_OBJ for unmergeable caches Content-Language: en-US To: Harry Yoo , Andrew Morton Cc: Christoph Lameter , David Rientjes , Roman Gushchin , Muchun Song , Shakeel Butt , Michal Hocko , Yeoreum Yun , Johannes Weiner , Suren Baghdasaryan , Hai Li , linux-mm@kvack.org References: <20260127103151.21883-1-harry.yoo@oracle.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: <20260127103151.21883-1-harry.yoo@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: C14F9180007 X-Stat-Signature: ntaprbo4fmioyzx7rjwekzth8w4sd9t9 X-Rspam-User: X-HE-Tag: 1769533573-828517 X-HE-Meta: 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 CEuBcBTr BPd+eoPgLwgLHQYhJRhB8w4Mkyd9vA15i3z4mLrbGhrcyAI3nOaag1vARmw6prbmRRqfPTPFWxPKVrlGEcd7vR+oMTNZY9BRzbDNYcIj8R2IlPEfoTkfKoA0pmRE9fiG7dcdBagbr415l71FP9+9PCN96rVDJ/bOqhM7Ug+hDf6T9Nv0sKqhKXbUfLZwIQ6yaBR2o/QnOWXjFS9+hwxQU2kUdxdyrjM7s8u/Ut+ZiTJRkIvnqGaOWYuLbqtEoleni6ToqqD7TCVLrpkE6hVNTDeVK34Euxy3uWG8M4yhH47WstYAYS8nT2zyKw6muvFH+ldLJl8M+x1ysINw= 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 1/27/26 11:31, Harry Yoo wrote: > While SLAB_OBJ_EXT_IN_OBJ allows to reduce memory overhead to account > slab objects, it prevents slab merging because merging can change > the metadata layout. > > As pointed out Vlastimil Babka, disabling merging solely for this memory > optimization may not be a net win, because disabling slab merging tends > to increase overall memory usage. > > So let's take a conservative approach and restrict SLAB_OBJ_EXT_IN_OBJ > to caches that are already unmergeable for other reasons. > > Ideally this should be part of the slab/for-7.0/obj_metadata branch, > but due to a conflict with slab/for-7.0/sheaves, I based it on > slab/for-next (be36abd97e52). > > Patch 1 factors out mergeability logic to slab_args_unmergeable(). > This is used to determine mergeability before the cache is created. > > Patch 2 uses the new function to allow SLAB_OBJ_EXT_IN_OBJ > only when merging is not allowed for other reasons. > > Harry Yoo (2): > mm/slab: factor out slab_args_unmergeable() > mm/slab: only allow SLAB_OBJ_EXT_IN_OBJ for unmergeable caches Thanks, applied to slab/for-next and reorganized the sub-branches a bit to prevent conflicts. > mm/slab.h | 1 + > mm/slab_common.c | 27 +++++++++++++++++---------- > mm/slub.c | 3 ++- > 3 files changed, 20 insertions(+), 11 deletions(-) >