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From: "David S. Miller" <davem@redhat.com>
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Date: Wed, 11 Jul 2001 16:07:01 -0700 (PDT)
To: Jes Sorensen <jes@sunsite.dk>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
        jgarzik@mandrakesoft.com (Jeff Garzik), bcrl@redhat.com (Ben LaHaise),
        hiren_mehta@agilent.com ("MEHTA,HIREN (A-SanJose,ex1)"),
        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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	<d3y9pv8ee5.fsf@lxplus015.cern.ch>
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Jes Sorensen writes:
 > The overhead is going be negligeble, the overhead of highmem itself is
 > much worse.

Once Jens's block layer stuff goes in, a lot of that overhead simply
disappears since the page cache need not bounce buffers.  The
networking can already technically cope with this too.

 > 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.

Not on x86 which is the current main benefactor of highmem.

Later,
David S. Miller
davem@redhat.com
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