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 5F2BAE9A03B for ; Thu, 19 Feb 2026 15:53:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A578B6B0005; Thu, 19 Feb 2026 10:53:19 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A053C6B0089; Thu, 19 Feb 2026 10:53:19 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 911046B008A; Thu, 19 Feb 2026 10:53:19 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 7F4FA6B0005 for ; Thu, 19 Feb 2026 10:53:19 -0500 (EST) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 2D6DC1A0602 for ; Thu, 19 Feb 2026 15:53:19 +0000 (UTC) X-FDA: 84461650518.02.43A147B Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf14.hostedemail.com (Postfix) with ESMTP id 595D8100014 for ; Thu, 19 Feb 2026 15:53:17 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=TD64GyPq; spf=pass (imf14.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 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=1771516397; 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=KUb1MPPUwyCxzj2goytrraqmabyZ5teqolKXmyMrBc0=; b=vAoiSU0mMZ3Qz2nJ2QoX2kmRp9xeJC/Q5iqp0m+QTj8SLjgquew5jAyBb07212RgHkCJ3b 2slYlDh/xjvwkEY5ucdR2O8V/VLhDtQ8tk+lJl/mu6HpXVyHwmv898pcZD2R47Yf4bdeq7 iysFwPowbzvHiZKTm/Clb8RTqE8b2jQ= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=TD64GyPq; spf=pass (imf14.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 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=1771516397; a=rsa-sha256; cv=none; b=wJBGTbBz8J5fcEwhrqr8sxqS5er3bMDoZhIglzAfeuzrgo4/Kqz0cC7JV3Z0OGDwusvR59 0okn9l/7muMBohfpNqeTTvWNJqm/x8RBpTUM8ovL95kYQTNgBoZ/19jKYA860kfIb0CNcM TKJ5qVVKDJQ3skBrRts9mjLYmI14KNc= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 8730660054; Thu, 19 Feb 2026 15:53:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 80E18C4CEF7; Thu, 19 Feb 2026 15:53:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771516396; bh=qFXqzjhF6S1cndDPwj4lCD499Qd5CkE/vgQLAzospSA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=TD64GyPqIFjUiJBCF3Qqom32GDBmy8sLsSlPBIRYxajLBWNG82r24/a0CI6JgeaCt Xtl22DieFcViEZYL8D8lqFSjrBnUJtL9eeK+8enxDDpSItJ1mQgm6vGfnTjVN3+Lmn GuZ3CZZFulPFXU9sMcCSRfdSMozNs9Ht8Z63Jqx9dfUxYoR75wsxVoWRPuDamOgcYl Fo6S00ejc00Xaq7MKaSTZVDx42NfOPwnbkq7upj9kObqNHbiuWv+B1THyWMvwy6920 cSduj/bWJHrcOUUM1jpJT3aHz+w+lPhGPC82kdGgnPkT58XOpI3XoazTQd9szWCTxl gaSj1zuIK+04Q== Message-ID: <0e2621c6-8829-46d1-9f29-81aebf365ba3@kernel.org> Date: Thu, 19 Feb 2026 16:53:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [LSF/MM/BPF TOPIC] 64k (or 16k) base page size on x86 To: Kiryl Shutsemau , Pedro Falcato Cc: lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, x86@kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Matthew Wilcox , Johannes Weiner , Usama Arif References: 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: pygj88ppjwon7rbqaaqxehdn8z1rrcij X-Rspam-User: X-Rspamd-Queue-Id: 595D8100014 X-Rspamd-Server: rspam01 X-HE-Tag: 1771516397-320094 X-HE-Meta: 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 YAwJ6lb0 8VZv+ahVztwDwU3wKxJLfad5Ky7pOcPzb+IbD0cl6m5Mcf33jg+pppnPpI0/PYQm12g+EyhtXYEE9MVS6JjJrxqbREhUDoXXOzJowdazoYgVm8V+Gh93+4dM7K/xVh03PNE7dOCksgWqQOdbLcTMhJfOeSYo3X+N/JQC0E3GFpl2AUvIrDYevK6jZMpJQ8yj/XiPdr96YOhN2VhEnliQPsyMkqrcBBzE/6hkCfAr2JHsOoe2SC7Y2MayBe1SR0FaL9z45 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 2/19/26 16:50, Kiryl Shutsemau wrote: > On Thu, Feb 19, 2026 at 03:33:47PM +0000, Pedro Falcato wrote: >> On Thu, Feb 19, 2026 at 03:08:51PM +0000, Kiryl Shutsemau wrote: >>> No, there's no new hardware (that I know of). I want to explore what page size >>> means. >>> >>> The kernel uses the same value - PAGE_SIZE - for two things: >>> >>> - the order-0 buddy allocation size; >>> >>> - the granularity of virtual address space mapping; >>> >>> I think we can benefit from separating these two meanings and allowing >>> order-0 allocations to be larger than the virtual address space covered by a >>> PTE entry. >>> >> >> Doesn't this idea make less sense these days, with mTHP? Simply by toggling one >> of the entries in /sys/kernel/mm/transparent_hugepage. > > mTHP is still best effort. This is way you don't need to care about > fragmentation, you will get your 64k page as long as you have free > memory. > >>> The main motivation is scalability. Managing memory on multi-terabyte >>> machines in 4k is suboptimal, to say the least. >>> >>> Potential benefits of the approach (assuming 64k pages): >>> >>> - The order-0 page size cuts struct page overhead by a factor of 16. From >>> ~1.6% of RAM to ~0.1%; >>> >>> - TLB wins on machines with TLB coalescing as long as mapping is naturally >>> aligned; >>> >>> - Order-5 allocation is 2M, resulting in less pressure on the zone lock; >>> >>> - 1G pages are within possibility for the buddy allocator - order-14 >>> allocation. It can open the road to 1G THPs. >>> >>> - As with THP, fewer pages - less pressure on the LRU lock; >> >> We could perhaps add a way to enforce a min_order globally on the page cache, >> as a way to address it. > > Raising min_order is not free. I puts more pressure on page allocator. > >> There are some points there which aren't addressed by mTHP work in any way >> (1G THPs for one), others which are being addressed separately (memdesc work >> trying to cut down on struct page overhead). >> >> (I also don't understand your point about order-5 allocation, AFAIK pcp will >> cache up to COSTLY_ORDER (3) and PMD order, but I'm probably not seeing the >> full picture) > > With higher base page size, page allocator doesn't need to do as much > work to merge/split buddy pages. So serving the same 2M as order-5 is > cheaper than order-9. I think the idea is that if most of your allocations (anon + pagecache) are 64k instead of 4k, on average, you'll just naturally do less merging splitting. -- Cheers, David