From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 8B9F76B024D for ; Thu, 22 Jul 2010 00:30:48 -0400 (EDT) Date: Wed, 21 Jul 2010 21:30:34 -0700 From: Zach Pfeffer Subject: Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device memory management Message-ID: <20100722043034.GC22559@codeaurora.org> References: <20100715014148.GC2239@codeaurora.org> <20100719082213.GA7421@n2100.arm.linux.org.uk> <20100720221959.GC12250@codeaurora.org> <20100721104356S.fujita.tomonori@lab.ntt.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100721104356S.fujita.tomonori@lab.ntt.co.jp> Sender: owner-linux-mm@kvack.org To: FUJITA Tomonori Cc: linux@arm.linux.org.uk, ebiederm@xmission.com, linux-arch@vger.kernel.org, dwalker@codeaurora.org, mel@csn.ul.ie, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, andi@firstfloor.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org List-ID: On Wed, Jul 21, 2010 at 10:44:37AM +0900, FUJITA Tomonori wrote: > On Tue, 20 Jul 2010 15:20:01 -0700 > Zach Pfeffer wrote: > > > > I'm not saying that it's reasonable to pass (or even allocate) a 1MB > > > buffer via the DMA API. > > > > But given a bunch of large chunks of memory, is there any API that can > > manage them (asked this on the other thread as well)? > > What is the problem about mapping a 1MB buffer with the DMA API? > > Possibly, an IOMMU can't find space for 1MB but it's not the problem > of the DMA API. This goes to the nub of the issue. We need a lot of 1 MB physically contiguous chunks. The system is going to fragment and we'll never get our 12 1 MB chunks that we'll need, since the DMA API allocator uses the system pool it will never succeed. For this reason we reserve a pool of 1 MB chunks (and 16 MB, 64 KB etc...) to satisfy our requests. This same use case is seen on most embedded "media" engines that are getting built today. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org