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[35.189.192.250]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a19f249692sm172738315e9.3.2026.10.12.07.49.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Oct 2026 07:49:26 -0700 (PDT) Date: Mon, 12 Oct 2026 14:49:22 +0000 From: Mostafa Saleh To: "David Hildenbrand (Arm)" Cc: Luigi Rizzo , 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 Subject: Re: [RFC: DMA_PMD 00/22] DMA_PMD: PMD_SIZE-backed IO buffer pools Message-ID: References: <20261003212241.3432303-1-lrizzo@google.com> <0cc1cac1-a500-489b-9c1b-b49598b5550b@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0cc1cac1-a500-489b-9c1b-b49598b5550b@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1AE75100005 X-Stat-Signature: 1hzt88mn5st4ez5hj9s5wug39i3ch3ua X-HE-Tag: 1791816568-56118 X-HE-Meta: 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 HyAr25Nh beYIX1JmOrOk3yV7GxmlgqTZcrHR4pe29+AssSKp7A+S2CmJujXfiZ4fYQmVmQnuM36tNIdAoOIQGOCJSfWDvXfUMcUqb4nHABNDreKeVh1q4fpr+jf4vPDt4q1H1xSdnrpl7S6+irTzZZRCYENbdSsElcfr4blG2QPpJKe0vk7q/Uf/HYR4eXm7b1Q3agebTGMX1vLhNAZwETNweSNBjW93c6Iu/ZMaWzJon2zSLtBDNvFPAILhZ972RQXmL3eN+ojea1f8jJfPv5Y7p0NT1uq7TqUKgOfMNASTbtEytbnpbW9GUNzYfWQpNVzawlopGwWeUsP/mPU4PyD73xJXMJTjb9q9HtVp4UqTI4tfqPSWnMxWtJ8PlccBlcUbnMz5QQzTxE7ImVoKmculugVZcp2xA+QiQGzZF1IiyN3M7QbQ8eZo2ftMirmeZ9FsnE0f+euNcSDgqaWVE3ro+tMXRcIOnVSpTWxQ4Xx21vCFPLXTNwx0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Oct 12, 2026 at 03:51:39PM +0200, 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)? +1 I raised the same point in the LPC talk. AFAIK, this series tries to solve both IOTLB pressure and CoCo bouncing at the same time which might be too strict; as for CoCo there is no actual IOMMU, so there is no sizing constraint. Also to reduce bouncing, I think it is sufficient to use the SWIOTLB instead of having a new pool + recycling, the tricky part is how to abstract that to client drivers as this would be needed beyond SKB. Thanks, Mostafa > > -- > Cheers, > > David >