linux-kernel - Re: [RFC 3/3] mm: iommu: The Virtual Contiguous Memory Manager

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Date:	Sat, 10 Jul 2010 16:36:35 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Zach Pfeffer <zpfeffer@...eaurora.org>
Cc:	Hari Kanigeri <hari.kanigeri@...il.com>,
	Daniel Walker <dwalker@...eaurora.org>,
	Andi Kleen <andi@...stfloor.org>,
	Randy Dunlap <randy.dunlap@...cle.com>, mel@....ul.ie,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 3/3] mm: iommu: The Virtual Contiguous Memory Manager

On Fri, Jul 02, 2010 at 12:09:02AM -0700, Zach Pfeffer wrote:
> Hari Kanigeri wrote:
> >> He demonstrated the usage of his code in one of the emails he sent out
> >> initially. Did you go over that, and what (or how many) step would you
> >> use with the current code to do the same thing?
> > 
> > -- So is this patch set adding layers and abstractions to help the User ?
> > 
> > If the idea is to share some memory across multiple devices, I guess
> > you can achieve the same by calling the map function provided by iommu
> > module and sharing the mapped address to the 10's or 100's of devices
> > to access the buffers. You would only need a dedicated virtual pool
> > per IOMMU device to manage its virtual memory allocations.
> 
> Yeah, you can do that. My idea is to get away from explicit addressing
> and encapsulate the "device address to physical address" link into a
> mapping.

The DMA-API already does this with the help of IOMMUs if they are
present. What is the benefit of your approach over that?

	Joerg

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