linux-kernel - Re: [PATCH] usb: fix number of mapped SG DMA entries

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Message-ID: <4EEA1EDD.9000609@linutronix.de>
Date:	Thu, 15 Dec 2011 17:22:53 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Clemens Ladisch <clemens@...isch.de>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: fix number of mapped SG DMA entries

On 12/15/2011 05:01 PM, Alan Stern wrote:

>> Is there anything special you do to get into this kind of situation?
>> Like 16GiB of memory on 32bit with highmem and a brutal disk/io test
>> case so?
>
> As I understand it, the typical case is that two SG entries in a row
> refer to adjacent pages of physical memory.  The mapping routine then
> collapses them into a single entry referring to all the pages.
>
> However, this is not the sort of thing you can deliberately cause,
> unless you set up your SG list by hand.

Thanks, both of you for the explanation.

>
> Alan Stern

Sebastian
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