linux-kernel - Re: [LKML] Re: USB transfer_buffer allocations on 64bit systems

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Message-ID: <20100412104858.GT30801@buzzloop.caiaq.de>
Date:	Mon, 12 Apr 2010 12:48:58 +0200
From:	Daniel Mack <daniel@...aq.de>
To:	Robert Hancock <hancockrwd@...il.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Pedro Ribeiro <pedrib@...il.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Greg KH <gregkh@...e.de>,
	alsa-devel@...a-project.org, linux-usb@...r.kernel.org
Subject: Re: [LKML] Re: USB transfer_buffer allocations on 64bit systems

On Fri, Apr 09, 2010 at 04:11:52PM -0600, Robert Hancock wrote:
> On Fri, Apr 9, 2010 at 3:23 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> > On Fri, 9 Apr 2010, Konrad Rzeszutek Wilk wrote:
> >
> >> On Fri, Apr 09, 2010 at 03:34:06PM -0400, Alan Stern wrote:
> >> > On Fri, 9 Apr 2010, Pedro Ribeiro wrote:
> >> >
> >> > > > The DMA pointers do indeed look sane. I wanted to take a deeper look at
> >> > > > this and set up a 64bit system today. However, I fail to see the problem
> >> > > > here. Pedro, how much RAM does your machine have installed?
> >> >
> >> > > It has 4 GB.
> >> >
> >> > That means DMA mapping cannot be the cause of the problem.  :-(
> >>
> >> That isn't entirely true. The BIOS usually allocates a 256 MB ACPI/PCI hole
> >> that is under the 4GB.
> >>
> >> So end up with 3.7 GB, then the 256MB hole, and then right above the 4GB
> >> you the the remaining memory: 4.3GB.
> >
> > How can Pedro find out what physical addresses are in use on his
> > system?
> 
> If you have 4GB of RAM then almost certainly you have memory located
> at addresses over 4GB. If you look at the e820 memory map printed at
> the start of dmesg on bootup and see entries with addresses of
> 100000000 or higher reported as usable, then this is the case.

Pedro, can you provide your dmesg output, please? I installed 5GB or RAM
to my machine now, and even with your .config, I can't see the problem.

Daniel

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