From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Lameter <cl@linux-foundation.org>
Date: Tue, 11 Nov 2008 20:34:21 +0000
Subject: Re: [Q] Why does dma_alloc_coherent() of ia64 GFP_DMA?
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To: Yasunori Goto <y-goto@jp.fujitsu.com>
Cc: "Luck, Tony" <tony.luck@intel.com>, FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>, linux-ia64@vger.kernel.org, Linux Kernel ML <linux-kernel@vger.kernel.org>, Joerg Roedel <joerg.roedel@amd.com>

On Tue, 11 Nov 2008, Yasunori Goto wrote:

> But our box supports both of 32bit I/O and 64bit I/O without IOMMU.
> Is it abnormal platform? New interface is necessary for our box like Altix?

No its like x86 with the GFP_DMA zone for < 16M addresses. The special
memory creates an imbalance that sometimes leads to weird VM behavior. I'd
make sure to set GFP_DMA only for devices that actually require < 4GB
memory and only use it if no IOMMU like stuff is available. Its best to
not use GFP_DMA.