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[213.95.11.211]) by mx.google.com with ESMTPS id q4si2746852wrj.148.2019.06.14.08.06.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Jun 2019 08:06:27 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of hch@lst.de designates 213.95.11.211 as permitted sender) client-ip=213.95.11.211; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of hch@lst.de designates 213.95.11.211 as permitted sender) smtp.mailfrom=hch@lst.de Received: by newverein.lst.de (Postfix, from userid 2407) id 9BFFD68AFE; Fri, 14 Jun 2019 17:05:58 +0200 (CEST) Date: Fri, 14 Jun 2019 17:05:58 +0200 From: 'Christoph Hellwig' To: David Laight Cc: 'Christoph Hellwig' , Maarten Lankhorst , Maxime Ripard , Sean Paul , David Airlie , Daniel Vetter , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Ian Abbott , H Hartley Sweeten , Intel Linux Wireless , "moderated list:ARM PORT" , "dri-devel@lists.freedesktop.org" , "intel-gfx@lists.freedesktop.org" , "linux-rdma@vger.kernel.org" , "linux-media@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "linux-s390@vger.kernel.org" , "devel@driverdev.osuosl.org" , "linux-mm@kvack.org" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 16/16] dma-mapping: use exact allocation in dma_alloc_contiguous Message-ID: <20190614150558.GA9402@lst.de> References: <20190614134726.3827-1-hch@lst.de> <20190614134726.3827-17-hch@lst.de> <20190614145001.GB9088@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) 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: On Fri, Jun 14, 2019 at 03:01:22PM +0000, David Laight wrote: > I'm pretty sure there is a lot of code out there that makes that assumption. > Without it many drivers will have to allocate almost double the > amount of memory they actually need in order to get the required alignment. > So instead of saving memory you'll actually make more be used. That code would already be broken on a lot of Linux platforms.