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 BAC2ACA9ED0 for ; Mon, 12 Oct 2026 19:44:09 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A6C916B008A; Mon, 12 Oct 2026 15:44:08 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A1D756B008C; Mon, 12 Oct 2026 15:44:08 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 90D796B0092; Mon, 12 Oct 2026 15:44:08 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 6219D6B008A for ; Mon, 12 Oct 2026 15:44:08 -0400 (EDT) Received: from smtpin05.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 4A576120A1E for ; Mon, 12 Oct 2026 19:44:06 +0000 (UTC) X-FDA: 85315000092.05.ED2C13C Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf27.hostedemail.com (Postfix) with ESMTP id 80D1940002 for ; Mon, 12 Oct 2026 19:44:04 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=HBvJzKuB; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf27.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1791834244; 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=dGLjQMre0HMGUZXG9eppSTB0wCfCdRy2DDP9ymJkK9U=; b=45qAHYjUp2/1iDUqXvdK9shWOADs9kmUMGOZ0tPYdT+iK3NViddAHnFQzlvJrwVgkaimWq cVq/o0Zpt5HaCgUUnFCytR6NejZNU+vd1fxCo6tD9EJiS85Zu3uABZhMhRYR2J8y3RxDnf kBdF3YKO5vgbCJo6Ma7AawCMLjG6OUw= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=HBvJzKuB; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf27.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1791834244; b=WTGu60JbU6U15dWztk0UwuTGZ6Rc8HkF76W91BaOp5l3JgKLIr0AvVGUiByNuMQgWMS3Dg 5+6V7OxOK57oe0dDTN/MO81XXWO/zFJmazLYCTXCG8LUiuQxy+nrv1Z8qaCzSGcnB8JMkz bNxe+fy+4vTt7q1/C0enNtFuBihqL/Y= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id E4FE240179; Mon, 12 Oct 2026 19:44:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E77A11F0089B; Mon, 12 Oct 2026 19:43:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791834242; bh=dGLjQMre0HMGUZXG9eppSTB0wCfCdRy2DDP9ymJkK9U=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HBvJzKuBOdeBqh/QLKaqbF4vvScglNF1iPQzZnras/u1vdP8rIsJVOAlS4mVUbJtV UmZW+8j78SfxSmWKbwA6OBme8ceC+KRnzfW0KF/H2rwJqaEMIzGLsMczRgu5h4k9YB i28BL29d1QfoM5ZN1D7Nc7ZYnFYMFufPkNIhwA/D2t39zLDFhnB/PNYxRk3AAOhG0N Uw4qb3awkuboFPoF++jrktejbNGLI4kmDMuVMGmwTQ2IduoR6c+FQ+T8YCd4gdldE9 n/NjaVoFm+8Cn8APSaUjyNSGCZvSBWwi6e6v+s7K8pAPIjNWvWujPT6uAywcOtkePv Uu2rgqxwodJ9A== Message-ID: Date: Mon, 12 Oct 2026 21:43:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC: DMA_PMD 00/22] DMA_PMD: PMD_SIZE-backed IO buffer pools To: Luigi Rizzo Cc: Luigi Rizzo , Joerg Roedel , Will Deacon , Robin Murphy , Christoph Hellwig , Marek Szyprowski , Andrew Morton , Vlastimil Babka , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Greg Kroah-Hartman , "Rafael J . Wysocki" , Danilo Krummrich , Jonathan Corbet , Jesper Dangaard Brouer , Ilias Apalodimas , Willem de Bruijn , Kuniyuki Iwashima , Joshua Washington , Harshitha Ramamurthy , Saeed Mahameed , Tariq Toukan , Tony Nguyen , Przemek Kitszel , Alexander Lobakin , Michael Chan , Pavan Chebbi , iommu@lists.linux.dev, netdev@vger.kernel.org, linux-mm@kvack.org, driver-core@lists.linux.dev, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261003212241.3432303-1-lrizzo@google.com> <0cc1cac1-a500-489b-9c1b-b49598b5550b@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 80D1940002 X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: e5igccjkjbgo9hrxbfybug4qd9fdy5wb X-HE-Tag: 1791834244-789436 X-HE-Meta: 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 yW6hTFK9 JOyq0NK93dLhwDAv0wZ7VxPejDq04+WVBPSLIkEkRJ8OSQt7VmtfYnn2+OUyl0Vdx3gh9hi2Wn3kcZx/xOxBa7+bvzfYZxIeOIVrCA40f8HnRy0sP1pXY0PoZUN4pX3zgZYgvldWuB/ZkhlduSC/UFXEppmdkpcio8s8n1wTtHMRKryaJfItzo9mja0wB9ifznwxNxhSW+TXU5mNaDS/06+pMoRjmf34oEThA9ve9fV4W655ng3bXGl5laQt1Bsg11/jUl6ViY/ROioOZLdXWP4O98BWtnTm4Jk9+LjU+7pFx+s42Da27eanIgO/P5LjfOVqw1OvkF8VpMWDt80sdlMYRfsdrnPlX9/fNvQXQuDgvqSaiprGQ+6Eo9NhaHDuJ5ysmDxo/hhQ4z2uEzQV6untLqze8vN8BAz8twCvnb636PPc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/12/26 16:45, Luigi Rizzo wrote: > On Mon, Oct 12, 2026 at 3:51 PM David Hildenbrand (Arm) > wrote: >> >> On 10/3/26 23:22, Luigi Rizzo wrote: >>> Here is a subsystem called DMA_PMD on which I would like feedback on >>> architecture, possible enhancements, or kernel components that could be >>> reused to avoid duplication. >> >> Here is a feedback to a subsystem called DMA_PMD ;) >> >> Why is basing this on PMDs (and embedding it in the name) the right approach? >> >> On architctures with large PMDs (512 MiB on arm64 with 64k), would we really >> want to use 512 MiB pages, or rather something smaller (e.g., 2 MiB) that might >> possibly also have TLB benefits (cont-pte)? > > I had to call it something... an earlier prototype used the name IOMMU_2M, > but I didn't want to suggest that the design was limited to 2M (it is not). > > Aside from the name, the _current_ prototype restricts to 2M allocations, > exactly because too large units are expensive and wasteful. > > In the code, decoupling the allocation size from the PMD size is trivial. Yeah, we should do that. We should probably just find a way to describe that this is a POOL that focuses on physical contiguity in some configured granularity. -- Cheers, David