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page cache of individual fs Content-Language: en-US To: Adrian Vovk , Dave Chinner Cc: Jan Kara , Matthew Wilcox , Christian Brauner , lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-btrfs@vger.kernel.org, linux-block@vger.kernel.org, Christoph Hellwig References: <20240116-tagelang-zugnummer-349edd1b5792@brauner> <20240116114519.jcktectmk2thgagw@quack3> <20240117-tupfen-unqualifiziert-173af9bc68c8@brauner> <20240117143528.idmyeadhf4yzs5ck@quack3> <3107a023-3173-4b3d-9623-71812b1e7eb6@gmail.com> <20240215135709.4zmfb7qlerztbq6b@quack3> <10c3b162-265b-442b-80e9-8563c0168a8b@gmail.com> From: John Hubbard In-Reply-To: <10c3b162-265b-442b-80e9-8563c0168a8b@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SJ0PR03CA0024.namprd03.prod.outlook.com (2603:10b6:a03:33a::29) To BY5PR12MB4130.namprd12.prod.outlook.com (2603:10b6:a03:20b::16) MIME-Version: 1.0 X-MS-PublicTrafficType: Email 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eCIUBGKqCo5j/LLgz6Go1xTNJTXJBxccLcsvGb+1g49wxP4ypcl+P0fK1fpTnMZIu9GWeG6duSjbKnhYkB7ndsX9X/WE7Cz0dtiftljs2y3bSGsdpsm8UsL2lIGX5E4GuMgdPz19mwoEPOSCrwSsPozey+2zpUEMxc0Q9XuLImYGSiJYKjQ3Jt07ZmcjI5lIUY3hbjrCB5KEOH78XEbEVUWPZ0z6rWSnOTMy+ntb6Cr5QWVOjYy6lyk388AADbe8Q5sGRxhL1L5sPsV2gpfXrCt7QJsqy++nvTEbwXEcxgrH6IMI= 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 2/15/24 17:14, Adrian Vovk wrote: ... >> Typical distro configuration is: >> >> $ sudo dmesg |grep auto-init >> [    0.018882] mem auto-init: stack:all(zero), heap alloc:on, heap >> free:off >> $ >> >> So this kernel zeroes all stack memory, page and heap memory on >> allocation, and does nothing on free... > > I see. Thank you for all the information. > > So ~5% performance penalty isn't trivial, especially to protect against And it's more like 600% or more, on some systems. For example, imagine if someone had a memory-coherent system that included both CPUs and GPUs, each with their own NUMA memory nodes. The GPU has fast DMA engines that can zero a lot of that memory very very quickly, order(s) of magnitude faster than the CPU can clear it. So, the GPU driver is going to clear that memory before handing it out to user space, and all is well so far. But init_on_alloc forces the CPU to clear the memory first, because of the belief here that this is somehow required in order to get defense in depth. (True, if you can convince yourself that some parts of the kernel are in a different trust boundary than others. I lack faith here and am not a believer in such make belief boundaries.) Anyway, this situation has wasted much time, and at this point, I wish I could delete the whole init_on_alloc feature. Just in case you wanted an alt perspective. :) thanks, -- John Hubbard NVIDIA