linux-kernel - Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device memory management

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Date:	Thu, 22 Jul 2010 09:28:20 -0700
From:	Zach Pfeffer <zpfeffer@...eaurora.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	ebiederm@...ssion.com, linux-arch@...r.kernel.org,
	dwalker@...eaurora.org, mel@....ul.ie,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, andi@...stfloor.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device
 memory management

On Thu, Jul 22, 2010 at 08:39:17AM +0100, Russell King - ARM Linux wrote:
> On Wed, Jul 21, 2010 at 09:30:34PM -0700, Zach Pfeffer wrote:
> > 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.
> 
> By the "DMA API allocator" I assume you mean the coherent DMA interface,
> The DMA coherent API and DMA streaming APIs are two separate sub-interfaces
> of the DMA API and are not dependent on each other.

I didn't know that, but yes. As far as I can tell they both allocate
memory from the VM. We'd need a way to hook in our our own minimized
mapping allocator.
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