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 19AA9CA9ED2 for ; Tue, 13 Oct 2026 10:42:21 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 343AA6B008A; Tue, 13 Oct 2026 06:42:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2F3D36B008C; Tue, 13 Oct 2026 06:42:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1E3DF6B009B; Tue, 13 Oct 2026 06:42:20 -0400 (EDT) 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 ED51E6B008A for ; Tue, 13 Oct 2026 06:42:19 -0400 (EDT) Received: from smtpin04.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 897CFA0906 for ; Tue, 13 Oct 2026 10:42:19 +0000 (UTC) X-FDA: 85317263598.04.5CBF2AE Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf21.hostedemail.com (Postfix) with ESMTP id AF7421C0004 for ; Tue, 13 Oct 2026 10:42:17 +0000 (UTC) Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=arm.com header.s=foss header.b=p4vMjRtm; spf=pass (imf21.hostedemail.com: domain of robin.murphy@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=robin.murphy@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1791888137; b=uHU/2Uy0/RB+GLNprTrACiUI5ExTnv0y5PtnHZNMt4v3PaQ0OL3LP6aiIgpVG/XVQTXypB tk4JVjRKs9DHZTooaMh7P4xWrvIlSQBVfIslLvyxYY+Q45VbZaHtFxJaI7CZxJ5Cv6/Wvl Z60fmvhm0cW3NMj6KPv26hsBbnMcLZg= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=arm.com header.s=foss header.b=p4vMjRtm; spf=pass (imf21.hostedemail.com: domain of robin.murphy@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=robin.murphy@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1791888137; 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=oD+XjwWNpVZKnPMgWXiYNmFqb79UfbIuRAu6qcSERgs=; b=jJq6rQuo2ZEFStl7Wtm8rA2PCYJIXFES7jbb+SDzmZmZXKUNKnl/sa2uUMAMFgVGnTiyRQ aaHvKjagCJ57We0+YMa8CdxYuyasb/lo0WKusbFqTYjmR4p+IRr0F1YTt5UFFzw2n3fBoH mFyxIlLNjH+LrGZxJVj9McLPie2+0JM= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 53FBA169C; Tue, 13 Oct 2026 03:42:13 -0700 (PDT) Received: from [10.2.212.23] (e121345-lin.cambridge.arm.com [10.2.212.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C226D3F7B4; Tue, 13 Oct 2026 03:42:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1791888136; bh=W9IOmZd6NCBQxQe8yp/0nFe31/tEy/JGEmdFhfz3Zx0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=p4vMjRtm+hGJY8UPjqMDOtxJKflXmrP2vqY/17xouBvpxZsfR430vOeHQp+g4HZHp i7cTDvCFclitDTgkIqF0/Rs5AUZgo0y+FddOHuWp92YB0Xjt5EVyzFCvtHFSv8ObTr iK08tMyzkAMpaUd65pUDChJk7GDyTxVjCmLAWF0c= Message-ID: <4fda41ed-741b-4c5f-ae83-e3ea5a447441@arm.com> Date: Tue, 13 Oct 2026 11:42:09 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC: DMA_PMD 00/22] DMA_PMD: PMD_SIZE-backed IO buffer pools To: "David Hildenbrand (Arm)" , Luigi Rizzo Cc: Luigi Rizzo , Joerg Roedel , Will Deacon , 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: Robin Murphy Content-Language: en-GB In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: AF7421C0004 X-Rspam-User: X-Stat-Signature: roah7baw33i3ra9n167943bo96b1m7if X-HE-Tag: 1791888137-411572 X-HE-Meta: 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 WK8tLdeE ROT93awjpNtnGad/k9KsamNY2uIdm9FWRrDdcGgXzeo/Lx8x4FajobNHuJLkdYrHSBYA8Qeuot0Q/k1oM/HywFCSa+NxUJ3KyibW7hXc7Ghbi5dxrcFGigVKTccbTqhljaqN9Y9BCI1XsRRWuy8isEXnv0YOLBIoA/zrlMNnMgklffW0Pftq5l4z5zLQvwXUfvrc1avSsuVAcn9omL16t96N+O9PJyFecY/auzo+8n6EprxqOkLrCm7WDR6HQKU9Fhgf3PH994kif0d75IaIokuN+ANbBnPWroqX0yNrHIt6x74ho/620y7vWmqBlbEYC4zTH0TL8q92kRu7zluvAQGq8fPMWmjYdfEYOsf516mIt+6RdS3YKBlihTvB6F6PMNoHp0c6M/878dHWgHotwFuMmAg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/10/2026 8:43 pm, David Hildenbrand (Arm) wrote: > 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. And since it's intended for DMA we could call it dma_pool and oh look it already exists... Sure the current implementation is capped at PAGE_SIZE for allocation (and thus mapping too), but I don't see why that couldn't just be made more flexible. Thanks, Robin.