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Fri, 30 May 2025 10:31:36 +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 pQH1AQiJOWh3BAAAD6G6ig (envelope-from ); Fri, 30 May 2025 10:31:36 +0000 Message-ID: <0aeb6d8b-2abb-43a7-b47d-448f37f8a3bf@suse.cz> Date: Fri, 30 May 2025 12:31:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [DISCUSSION] proposed mctl() API Content-Language: en-US To: Johannes Weiner , Matthew Wilcox Cc: Lorenzo Stoakes , Andrew Morton , Shakeel Butt , "Liam R . Howlett" , David Hildenbrand , Jann Horn , Arnd Bergmann , Christian Brauner , SeongJae Park , Usama Arif , Mike Rapoport , Barry Song <21cnbao@gmail.com>, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Pedro Falcato References: <85778a76-7dc8-4ea8-8827-acb45f74ee05@lucifer.local> <20250529211423.GA1271329@cmpxchg.org> 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: <20250529211423.GA1271329@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: B8AD91C0007 X-Stat-Signature: gh8dh98u6iikkm9yi6dz33e6nzhitkhr X-Rspam-User: X-HE-Tag: 1748601097-417762 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 5/29/25 23:14, Johannes Weiner wrote: > On Thu, May 29, 2025 at 04:28:46PM +0100, Matthew Wilcox wrote: >> Barry's problem is that we're all nervous about possibly regressing >> performance on some unknown workloads. Just try Barry's proposal, see >> if anyone actually compains or if we're just afraid of our own shadows. > > I actually explained why I think this is a terrible idea. But okay, I > tried the patch anyway. > > This is 'git log' on a hot kernel repo after a large IO stream: > > VANILLA BARRY > Real time 49.93 ( +0.00%) 60.36 ( +20.48%) > User time 32.10 ( +0.00%) 32.09 ( -0.04%) > System time 14.41 ( +0.00%) 14.64 ( +1.50%) > pgmajfault 9227.00 ( +0.00%) 18390.00 ( +99.30%) > workingset_refault_file 184.00 ( +0.00%) 236899.00 (+127954.05%) > > Clearly we can't generally ignore page cache hits just because the > mmaps() are intermittent. > > The whole point is to cache across processes and their various > apertures into a common, long-lived filesystem space. > > Barry knows something about the relationship between certain processes > and certain files that he could exploit with MADV_COLD-on-exit > semantics. But that's not something the kernel can safely assume. Not > without defeating the page cache for an entire class of file accesses. I've just read the previous threads about Barry's proposal and if doing this always isn't feasible, I'm wondering if memcg would be a better interface to opt-in for this kind of behavior than both prctl or mctl. I think at least conceptually it fits what memcg is doing? The question is if the implementation would be feasible, and if android puts apps in separate memcgs...