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From: Hans Petter Selasky <hselasky@c2i.net>
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Date: Fri, 17 Apr 2009 08:24:31 +0200
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Cc: Richard Todd <rmtodd@ichotolot.servalan.com>,
	Damian Gerow <dgerow@afflictions.org>
Subject: Re: ZFS checksum errors on umass(4) insertion
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On Friday 17 April 2009, Scott Long wrote:
>
> It could, and if that's happening, then some proactive measures should
> be taken by the usb code to generate buffers that won't bounce.  It
> would suck to have to go through the bounce code for every single
> keystroke or mouse movement.  I haven't looked at the new usb code,
> though, and I thought that the old code did a contigmalloc of some
> sort to avoid this.

USB uses an alignment of 1-byte for its data buffers. It should only bounce 
when the page the data buffer is residing on is above 4GB.

--HPS