From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D747DE9A03B for ; Thu, 19 Feb 2026 16:00:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 197B06B0005; Thu, 19 Feb 2026 11:00:29 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 11B866B0089; Thu, 19 Feb 2026 11:00:29 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F35BB6B008A; Thu, 19 Feb 2026 11:00:28 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id DCD666B0005 for ; Thu, 19 Feb 2026 11:00:28 -0500 (EST) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 85CE01B586E for ; Thu, 19 Feb 2026 16:00:28 +0000 (UTC) X-FDA: 84461668536.30.6AD0EC5 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf12.hostedemail.com (Postfix) with ESMTP id A0DEE40008 for ; Thu, 19 Feb 2026 16:00:26 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=VDS6Ww5p; spf=pass (imf12.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1771516826; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=s6K1Y2hYAQR9A928JdXRY41r2eMvsWf1aqdX9/1ul4A=; b=2TDsxG7sK1ppaNiVUmWsVKwo5Cvq66/u8BRC0hlGqiZzEw1Rf1MhdPluS/CDdF1FHD5D70 qpnWbKjx6tSh3kXCYBK2Es5RmeG9YlDG5ftVLLGPWjsNKP7vkOiACKTKBvEX4fQtpn8ooO RNh4tK8tMkHSAqx1/FxvSGK2hUk2JKI= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=VDS6Ww5p; spf=pass (imf12.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1771516826; a=rsa-sha256; cv=none; b=JORt4vLZcfS02Iq3qKWyaFwl13jtmMsBC0niI5G0Kpl7PzTjxUdQ8O5UGvFtb6ObbsJqD9 H7OfDsm8NG4rEl2yOFyRJKHG+jlSBKuLBUC9xqD4YVNdnaL3tcxKEdaTLLRwatidUiZFLG fyUdOkjf96lCvp4vwd2nKSXXuzPxxJI= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 9B05243F40; Thu, 19 Feb 2026 16:00:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3EC00C19421; Thu, 19 Feb 2026 16:00:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771516825; bh=6jRlSyeeOj3lGQGeEjhRS4KebTzltCXVjpVFvPwNnB4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=VDS6Ww5pRdeHoyx+dQBaH2T/gzDqZVoehxCCahiiC8L83aNazja+EkirM9s5yBvmL BIJcd3JRXxbi/C7/7msEVHe2vd5lNcvW0rvV9RGtlXmBbCFYIc1tAEnH77JWsfS3WY H4+xB7CloEPt8v/10pLOdCskg8aTCn6ltD4D2MVjBLzeWp2XXfKkfqqH5ZaNwh7yP6 kLIXs3KIAce1MraGX8VjE9kNIvHVseax27kkRgBiJlQa6keoVcpgjwx8u8/cPkCgIk uRDazFO25e/WwUyOe8ARZosjS19Nl66Y0MX9zxu7zP5+4zuD05ggHczIVGRi9qq+gQ cVyv07782rGCw== Message-ID: <3485c8c8-9bfc-4725-885a-626e79d0aebb@kernel.org> Date: Thu, 19 Feb 2026 17:00:19 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [LSF/MM/BPF TOPIC] Beyond 2MB: Why Terabyte-Scale Machines Need 1GB Transparent Huge Pages To: Usama Arif , "willy@infradead.org" , Lorenzo Stoakes , Zi Yan , Andrew Morton , lsf-pc@lists.linux-foundation.org, "linux-mm@kvack.org" Cc: Johannes Weiner , "riel@surriel.com" , Shakeel Butt , Kiryl Shutsemau , Barry Song , Dev Jain , Baolin Wang , Nico Pache , "Liam R . Howlett" , Ryan Roberts , Vlastimil Babka , Lance Yang , Frank van der Linden References: <540c5c13-9cfb-44ea-b18f-8e4abff30a01@linux.dev> 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: <540c5c13-9cfb-44ea-b18f-8e4abff30a01@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspam-User: X-Rspamd-Queue-Id: A0DEE40008 X-Stat-Signature: jpuu441owmyokqeic5oy5zzuuryf4u7a X-HE-Tag: 1771516826-504353 X-HE-Meta: U2FsdGVkX18Bnht/ZVVYNwn4fUtpqNS9XO9T/n3GpLL+nqa998vF9U9LJWF4GrJJnuXMkZgLxlAfIf9PoVugLxLoTUiDk7loNK9jbjeVK0MA2dDiIF3BvhsZ6JgtiaEEpvktujanBgARd8UBwN/GldJKkzaR1i04iDs7IsVlAGipDG6YsvioyrSGwPzKwYGr0cu2sMux+AxAp0DHZYCs5XagokS4xltq+8CvkwzeB2srx0zG04W257Wc4sFoNRy5QcRGonL/FAyHYZ+Z2byHIdsrXFUmIa5BRErZHXY1EBGK+xyQuX3aicLGIHnBuD9eRJ1g+SJbr5FVb/oXhrKsUdfrsHSr/FsNIvmW/WEvxrWxcqXTgxnRATTmho1/7ENG5ZY6BYxeBxbGsm5Sf3ZNqA9P6Iw4AcPjIYzoVr++lmxJ1nPOpQFaENxFbCl2phDc+5F0BGXscJO2mvxx4ickMMqha1mMRg8cvXmJa9ne7RC/E10zZowndaBLSt7ho9jMrX0nL/uTk0g3BrTp9GO1gDNkMV7jP+WZTv1mXNF/zWaYxS7SQW+I4pAlE8UoENsDL0dKB4nyGQ2g/WBn5dls7qpwYEStukxFLruJb5QWdhMDxj9TvY/Cftbo8ZlIadqEaDXEonU8RE1gXa5AWEsVdi2DG85pfDbSvdPy4NYDk/OtWybzvx7QkwQKZNdIqP5eEx4mRNCq8d8J3LTr8q96TN6n3Zl2vHgO+Tco3wmTG9DnwmKP4fpMPA2Wk7p4MhPfv/Er/XTVgg9+dyOYrHf3CBw0zqKk+JjEHw5umc1MSTGEVqssG590+iRxxuapUT9i4ismmgbuSChwAGRPGON1a9pwjCrLR7NzeqMapxjZiJAtThnHtY3QK3HrNMxSOAXjpazWn12XkRi8+eZ7kGFyGajIb1i8vk4QoKQ0osyEvK00whgjfk2JM1dthfyqnmdASTR3/6HQK7gf5P0qoix MUBXuTQc 8n2Gk 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: > > I see 1G THPs being opportunistically used ideally at the start of the application > or by the allocator (jemalloc/tcmalloc) when there is plenty of free memory > available and a greater chance of getting 1G THPs. > > Splitting strategy > ================== > > When PUD THP must be break -- for COW after fork, partial munmap, mprotect on > a subregion, or reclaim -- it splits directly from PUD to PTE level, converting > 1 PUD entry into 262,144 PTE entries. The ideal solution would be to split to > PMDs and only the necessary PMDs to PTEs. This is something that would hopefully > be possible with Davids proposal [3]. There once was this proposal where we would, instead of splitting a THP, migrate all memory away instead. That means, instead of splitting the 1 GiB THP, you would instead return it to the page allocator where somebody else could use it. However, we cannot easily do the same when remapping a 1 GiB THP to be mapped by PMDs etc. I think there are examples where that just doesn't work or is not desired. But I considered that in general (avoid folio_split()) an interesting approach. The remapping part is a bit different though. -- Cheers, David