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b=ixHulrZxrmJT9lfSwaDj4SWjTvLSrkbTPBYKU+Fg1+sffniB11uyw1qCzpuRdYiPk zUgv+2NJ40uemHK8XhXsJOpt4wt7YiN9kzADUr+JnCKuYxU9CiAYDCFpqxge7IYxBA JOxsmcRLr6fYAGMULodWLhhHGKphKgZXC0r3XPjg8BORNg3KNbXumftopqVU6lmYjj +I2KxYz8OU52dWkzagqLJVmx3afd77dfhk/xPqvnfRcwUGz4m+/PRGDT0e9nPlW0NG gY9nNDSFFWRR45lAQwhZXJphqNBH3T35d4hIu/LtSMOLiYLF0P1AdSGi3buftlb1PB NJjV3anxHrL/Q== Message-ID: Date: Mon, 7 Sep 2026 15:59:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: vmpressure: scale window size based on machine memory To: Taha Sezer , ljs@kernel.org, akpm@linux-foundation.org Cc: vbabka@kernel.org, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260831130316.448-1-tahasezer.is@gmail.com> <6a9673f4.cbade83c.66f7c.3d66@mx.google.com> 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: <6a9673f4.cbade83c.66f7c.3d66@mx.google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 85kdr1da3djhi93ojjr5yei1es5a1bnf X-Rspamd-Queue-Id: 693DB1C000A X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1788789546-875877 X-HE-Meta: U2FsdGVkX1/fkK2Pu7Nnwr8y7FKpzWd7xIjJapwFguHxoGysJHXz/gJTYXaZCxDk7uFJ4HW/+PaxqTbM8b8oECXf547D/ZrjNja4X3G/J1qZ/BBUfLfUt3VuHl1b5f0ED7PDWtEC3DkuJb9QMI9yLrvbfXxhlBeSVn8vH0mlGQsYGhrNROD/X3QoYJ2eDFqxOA4+8wwym5q8W8Cu+hb8+pP3repZ7cxpdBH9o6trYbSLD/HHqXmTpEwvQJFkE5jBZQuga6p1ci4Mt2fGCGKr6eOXyTWjiCzZqZenLze2IWp2WnvfhMiaF5HWJ5b///jm1JyHVjH6wFQqO24WkUWLv2I5jU5tE5jb0dO4DR1uHN4SQyU+pDJWdK8/nAjATELs7P+EpdeFycsEDZWe2lcxpBL9a6afdMaM0bv2qhMTj26ROtmGoRhkPz3Un55ZI9nWupbxGQTNmOOA+t9JZwuxbriPEnU8pLZvv/QZJS6I0iCK9wn05CN36FyOk28/fx2WIR2SRuujPDuSPXyd73xfCqCuDKsZhW3VujIMfByeSWBTODYEuRH0y47y8k8K2VjOBWSrl7k6epqtDE9JG+jXBPbV0SjSPRrolMxAcnqoyfuGtttgFAOm9DH/nQva6Q+LTJicm5XjoM0oydt8I7nZ8L1BvrOQ9ezKBnEw3D1ZzZVsaKwK5cLGE3A1X8+IYYH8fMlBD6gCF0wvXedJ36BGnAAlr0sLQx/HwRRFx8PFgr5ZBYptrui6YgC4oyWKHTqbf1dzuIfQt1ScGWipWiRrWvj0kqJcAc9mkiRQzTDrbU9w376wQkkU9YdTLIy26VC2RVjPwFAy/4zxuvZX1tbkRVjJNg3h0JPW7O0NafNJyCoCX6wWyIJTkZpiXKMKkj7Bv8ki1ikuhRj2S8vMCGddJWNAupIYKWk4h2CIX1HTs+n7bTjcF091Of5x0zLjDgrlFjAgXpzg1Lqw6GIbF/l Pgy/hxgS ssWuHyDDAHVRl9UzuOGsZlZxYilBgXplzxAB00M8CCcukzs//Yx7OSG38kJBmpXXWMLynlBkUFpRiAxIeoEG91XP+BjjQxTg/aFAzyEbT6S1rMiBivcwRtvVAqO+HqvEAlMCzHEie6KQs+5NFtkuWjchb/np16H6t7H2cXgD0O1lyMv2VWE91mmM0+VsGFTEW/rF4Mx6qYXntNQ38tKHAWiXne75RFPk2Ng5kY4pT75uxBido1tY/VpFfyrJV5gq9oimSiYaHSgRuGRWzXtCKGYnx9Vf0deP/68VHYVlWs68yEnW8/SMIiDMNRBeLaNfAAY0piqZRZEoTXHk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/1/26 08:43, Taha Sezer wrote: > Hi Lorenzo, Andrew, > > Thanks for the honest and thorough review. > > Lorenzo -- yes, I did use an AI coding assistant (Claude) to help > write this patch. I should have included an Assisted-by: tag from > the start and I apologise for the omission. That was a mistake on > my part, not an attempt to hide anything -- I simply was not aware of > the disclosure process for my first submission. > > Andrew -- you are absolutely right about the math. The original window > is SWAP_CLUSTER_MAX * 16 = 512 pages, and my formula clamp(fls(mem), > 4, 64) produces values well below 16 for every machine under ~8 TB. > The patch shrinks the window on virtually all real hardware, which is > the exact opposite of what the commit message promises. Embarrassing, > and I should have caught this before sending. > > For a bit of context on why I chose mm/: I have been writing a hobby > kernel from scratch (Caelum) that includes a VMM with COW and demand > paging, a slab allocator with NUMA-aware allocation, TLB shootdown > via IPI, and SMP boot -- so memory management is the area I am most > comfortable with. That said, comfortable with the concepts clearly > did not save me from a basic arithmetic mistake here, and I take full > responsibility for not verifying the output carefully enough. > > Before I send a v2, I would appreciate any guidance: > > 1. Is the general idea still worth pursuing -- scaling the window > logarithmically with total RAM using fls(), or do you think > the fixed 512-page window is fine as-is and this TODO is > better left alone? > > 2. If the approach is worth fixing: would keeping the original > multiplier of 16 as the floor (so the window only ever grows > beyond 512 pages) be the right direction, or would you prefer > a different scaling strategy entirely? > > 3. Any other advice for a first-time contributor on how to > approach mm/ patches more carefully? > > I will hold off on v2 until I hear back, so I do not waste anyone's > time with another half-baked attempt. The next version will include > a proper Assisted-by: Claude:claude-opus-4 tag. Note that we now prefer Assisted-by: LLM -- Cheers, David