From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794760843; b=i6mLpVa5Zu9JrqoLuHQVoEqEnvUx445WAcGdiqx4ic47hinzWnVSmVqanfwzhBaVMy63 zXJrJKxzpBWw+dreHlm6ah0QFhkpHZy1UDASZatCQZ/cMH0tt6M0WOwtXa8paXvZzPvbV jc71pFbzQ2O9BnHeATkRZ8dmz9uGk2gioKOZZxo2zJUbb0ypqpreFEEffQAFxNGuF4cGQ kKDZ0ATLmAX9Ruw9KWXnuYhxeBLDY/XkJWe5vjlY0fYu3EY8hR2765GlWC0dvC1tvuD5O +fsaUOxq49Es2Av3asrKa6t98calYeIhHWOEWCWLgch4GK9wp3qD2ri5v9ARr2xBCjw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794760843; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=u+CDFH8zAL7wgGtbRFmlbP0nitp9kr0fmBISA0T1p0A=; b=NHVtwjlwDHBM2PMCFdPj53l8z6SyS66HMlrAOPq5w6Q0o9ZmCnkzeoVULEMlH0cB97rU YLmRjFGQCPJAzZgiSSPmDLYjrwpbZXhc14t7Dr00nYOtWASsaIhsTJHCRpFsdvLDnALx/ t3LH/DkvPi0GEgFB4bl3Veq8x4YLmbUoLHT5GqBIzOth3Qi7HH2fWQYZa3q2xB4o/6jwY bHp2B49POP65ZuP7f92E5jsKpoCbdkmR3rsuns763+b24tK4exgJEx/Qk0pw6sMUTZqy2 hNEb8hPDUOc4uAb7zUUzXIbK570h7JaWPdJRhd32XgKrkoMByLZDeCB+Ysm77BUpgkQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=GASWgN6s; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 19267606A31E; Sun, 15 Nov 2026 16:40:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=GASWgN6s Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5AE3F1F000C4; Sun, 15 Nov 2026 16:40:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794760842; bh=u+CDFH8zAL7wgGtbRFmlbP0nitp9kr0fmBISA0T1p0A=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=GASWgN6st+wThFR8ljMWn0jEpKoCDnhja450JTeo/R52YP0MLytxoNmV5cCvcwFpO JpE5FnY1kNm97xMfTGykI5yGxYtWDDFjIm15LEjqlDGhvmZh2eJ3TquPNtIDDq/BAi X4bD4X048/7zuo6GgfJkiuJHDMSIABShwEXV1M7k6R4gb6s+iGH3d+J3SIJOG1L7sT SiZr9qLaL8+P/xG2NUj6qSbK61OKoW48tV1kP2lKTbvz4t2Fb1YYZlkox6ATxmUyD1 oU0e1C67qKhAA4bn8q7rMG7KTyHWc7CRCyhAOUKTU4ibLX+sWl0gLHT52wcHlioswV joWoQcgy8kgoA== Message-ID: <76fc4555-b458-491b-ba2c-ec030879dafe@kernel.org> Date: Sun, 15 Nov 2026 17:40:31 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] mm/mempolicy: limit shared policy ranges per inode To: "Gregory Price (Meta)" Cc: Hugh Dickins , Baolin Wang , Zi Yan , Joshua Hahn , Rakie Kim , Ying Huang , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Shuah Khan , Randy Dunlap , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org References: <20261113-mempolicy_limit-v1-0-16688b2644dc@kernel.org> <20261113-mempolicy_limit-v1-2-16688b2644dc@kernel.org> <179467808112.482102.13365594235443107281.b4-reply@b4> <70740a32-92f5-4425-8676-68863f3e44c3@kernel.org> <179468794889.482102.14066028910704780583.b4-reply@b4> 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: <179468794889.482102.14066028910704780583.b4-reply@b4> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/14/26 21:25, Gregory Price (Meta) wrote: > On 2026-11-14 21:16 +0100, David Hildenbrand (Arm) wrote: >> On 11/14/26 18:41, Gregory Price (Meta) wrote: >>> >>> Multi-task mappers were previously unlimited, but that seems like more >>> of a nasty unintended corner case - not a real feature. >>> >>> A single process is already limited on the number of vmas/policies based >>> on `max_map_count`, so it seems natural to just use max_map_count >>> directly, but I took a brief look at some distros and most seem to >>> ship a raised `max_map_count` (>1 million) by default). >>> >>> I tested that and even 1 million can cause a soft lockup. >>> >>> Not sure there's an easy solution here, we might have to rework the shm >>> policy locks. >> >> Do you know a single valid use case that's not solved by patch #1 and would >> trigger that many policies? >> >> Ai was not able to come up with anything for me. > > Just want to make sure the bases are covered. > Yes, and I'd be very happy to learn about use cases. Maybe we can let this stay in -next for a while before moving forward with this? > If others are ok with this change, it doesn't look unreasonable to me. > > Although I'd wonder whether just using max_map_count's limit instead of > adding a new toggle would just be cleaner and avoid adding a new uapi. I considered it but discarded that. Having 1mil on Fedora et al is not particularly helpful. Both are related but, in practice, completely separate concepts. -- Cheers, David