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Subject: Re: DMA memory limitation?
To: pvvvarma@techmas.hcltech.com (Vasu Varma P V)
Date: Thu, 5 Jul 2001 12:53:45 +0100 (BST)
Cc: linux-kernel@vger.kernel.org (kernel Linux)
In-Reply-To: <3B4453E6.F4342781@techmas.hcltech.com> from "Vasu Varma P V" at Jul 05, 2001 05:17:50 PM
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From: Alan Cox <alan@lxorguk.ukuu.org.uk>
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> Is there any limitation on DMA memory we can allocate using
> kmalloc(size, GFP_DMA)? I am not able to acquire more than
> 14MB of the mem using this on my PCI SMP box with 256MB ram.
> I think there is restriction on ISA boards of 16MB.

Yes. GFP_DMA allocates memory below 16Mbytes for ISA devices and that is
a physical wiring issue. For PCI devices you can allocate a lot more using
the pci_alloc_* and pci_map_* interface to allocate memory for PCI in a
CPU independant manner. It'll also then look after cache coherency issues
for you

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