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[142.167.56.70]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6fb35b20abasm63746496d6.1.2025.06.17.08.55.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Jun 2025 08:55:14 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1uRYeY-00000006WS6-1OTF; Tue, 17 Jun 2025 12:55:14 -0300 Date: Tue, 17 Jun 2025 12:55:14 -0300 From: Jason Gunthorpe To: Arnd Bergmann Cc: Christoph Hellwig , James Clark , Mark Brown , Vladimir Oltean , oe-kbuild-all@lists.linux.dev, Larisa Grigore , Frank Li , linux-spi@vger.kernel.org, imx@lists.linux.dev, linux-kernel@vger.kernel.org, kernel test robot , Marek Szyprowski , Robin Murphy , iommu@lists.linux.dev Subject: Re: [PATCH] dma-mapping: Stub out dma_{alloc,free,map}_pages() API Message-ID: <20250617155514.GC1376515@ziepe.ca> References: <7cfcf919-3c7d-4f0c-911f-697ea3141080@linaro.org> <20250616131346.GB29838@lst.de> <83855c1a-c128-4762-9d6b-e17f2c4c8820@linaro.org> <20250616131944.GA30260@lst.de> <9788991a-ac37-4fde-81db-c55035d00f27@app.fastmail.com> <20250617044833.GE1824@lst.de> <5de445aa-048b-4f60-9045-df5d45341436@app.fastmail.com> <76a8c896-d7ea-4471-99a2-34b3a7ac9804@app.fastmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <76a8c896-d7ea-4471-99a2-34b3a7ac9804@app.fastmail.com> On Tue, Jun 17, 2025 at 10:26:51AM +0200, Arnd Bergmann wrote: > On Tue, Jun 17, 2025, at 09:53, Arnd Bergmann wrote: > > > Between SH72xx/SH76xx, SUN3 and M68328, I believe the > > supported machines are all limited to between 1MB and 32MB in > > the maximum configuration, which is obviously extremely > > tight. > > I checked the exact numbers we're talking about here: enabling > CONFIG_HAS_DMA on rsk7269_defconfig adds 10KB of extra vmlinux > size, which doesn't seem too bad: > > text data bss dec hex filename > 3295084 1111396 112264 4518744 44f358 vmlinux-before > 3302836 1113652 112264 4528752 451a70 vmlinux-after Long ago I ran some numbers for an ancient PPC system: https://lore.kernel.org/all/20121119214922.GA5636@obsidianresearch.com/ The base smallest kernel was growing .text and a stripped down initrd at a rate of 1MB evey 6 years. Somehow I doubt that system (with 16MB ram I think it was) would even fit a v6.x kernel. v3.6 was already challenging. Even back then Greg was incredulous that an embedded system would run a 6 year newer kernel. Here we are contemplating a 20 year newer kernel? I think you have the right direction, we just removed !SMP support, removing !DMA also seems logical to me. Jason