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Date: Thu, 12 Jul 2001 09:54:21 +1200
From: Chris Wedgwood <cw@f00f.org>
To: Jes Sorensen <jes@sunsite.dk>
Cc: "David S. Miller" <davem@redhat.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Jeff Garzik <jgarzik@mandrakesoft.com>, Ben LaHaise <bcrl@redhat.com>,
        "\"MEHTA,HIREN (A-SanJose,ex1)\"" <hiren_mehta@agilent.com>,
        "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>
Subject: Re: (reposting) how to get DMA'able memory within 4GB on 64-bit m
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On Wed, Jul 11, 2001 at 09:16:50PM +0200, Jes Sorensen wrote:

    The overhead is going be negligeble, the overhead of highmem itself is
    much worse. Not to mention that today some dma_addr_t's might not be
    packed properly in data structure hence they ending up taking 8 bytes
    anyway.

What kind of packing makes a 32-bit value take 8-bytes on any
currently supported archicture? The worst-case I can think of is
7-bytes in the case of misaligned by 3 (e.g. __attribute__((packed))
struct blah { char foo[3]; long bar }; sort of thing).




  --cw
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