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Tsirkin" Cc: linux-kernel@vger.kernel.org, Miaohe Lin , Naoya Horiguchi , Andrew Morton , Oscar Salvador , Andi Kleen , Hidehiro Kawai , Rik van Riel , Vlastimil Babka , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Hao Li , Kiryl Shutsemau , Byungchul Park , linux-mm@kvack.org, linux-cxl@vger.kernel.org References: <0b5f8b4b-d7dc-4b79-9555-a5b36265f3a9@kernel.org> <20260629030657-mutt-send-email-mst@kernel.org> <4f5ba5d6-246c-4430-9737-e8dd8e4c5142@kernel.org> <20260629092856-mutt-send-email-mst@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260629092856-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: ituis1gdkadpj3qjj8adgq6w88rpi4aw X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 196D8A0005 X-HE-Tag: 1782768144-378182 X-HE-Meta: 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 tRQIJc8m +gmZNmTZ5snas13XxYbbKuIDQmPk8OPaSi+bSuZrY0q2Hju2js/382YBckdVREL9LxTelkBHHAbGwmZVu/uRc6ILxNeGDANungA8F5Pe0VDQTGdzvGvBCISkdj4jSiyYk+XMNmtuNrZn2TOPcQ33TKv/21vOrUkXyvjkgPm84VJbWPjB0iu8HELzAcySwIpP7yK7FpuqkpCW6T4h3yQjZCQZFYjX0KV09gUpuGeKiH6Hp9XgZ5HSo0kStGSjMFZeXbecQPB9ZqmwL0wPU08wH7hXo80GpYgFs6r2m45Nj5+fV2tWttDbZnjBi9+LXuStlDBJSyHa/Wq737ifkNPmHlY/GaA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: [...] > > And again, I'm really not sure fixing a theoretical race when memory > is failing is worth slowing the world by 0.1-1% for. > Fully agreed. I was hoping RCU was cheaper (I mean, we were once told that RCU read side locking is essentially for free ... well in some configs :) ) The question if we could optimize it reasonably enough ... > > From what I saw in my testing, if we allocate 4k pages > it's hidden by the overhead. With hp and thp it's measureably > worse than rcu on !preempt config. ... for example, by doing the rcu read lock + unlock around the for (i = 1; i < (1 << order); i++) { loop on the alloc path. But I suspect it's not going to make that much of a difference. I concluded, similar to Andi, that stop_machine() is too big of a hammer. I wonder if something could be built out of preempt_disable() and sync SMP calls. hmm :( -- Cheers, David