linux-kernel - Re: [PATCH] x86: avoid unnecessary low zone allocation in AMD IOMMU's alloc

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Message-ID: <20080910145249.GB24392@amd.com>
Date:	Wed, 10 Sep 2008 16:52:49 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu
Subject: Re: [PATCH] x86: avoid unnecessary low zone allocation in AMD IOMMU's alloc_coherent

On Wed, Sep 10, 2008 at 11:39:00PM +0900, FUJITA Tomonori wrote:
 
> btw, in tip/x86/iommu, GART's alloc_coherent always does virtual
> mappings to allocate a size-aligned memory (as DMA-mapping.txt
> defines).
> 
> Because someone strongly insisted, I modified GART's alloc_coherent to
> do so but as I said again and again, it's completely meaningless (only
> POWER IOMMU does it and drivers don't depend on such requirement).
> 
> I guess that it would be better to do virtual mappings only when
> necessary as the current mainline does since GART I/O space is
> precious in some systems. But I don't care much. What's your opinion
> (as a AMD developer)?

Very true. My original rewrite did the mapping only when necessary too.
What were the reasons to do the mapping always?

Joerg

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