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Date: Thu, 03 Feb 2011 12:37:40 -0800
From: Yinghai Lu <yinghai@kernel.org>
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To: Andrew Morton <akpm@linux-foundation.org>
CC: Ingo Molnar <mingo@elte.hu>, David Miller <davem@davemloft.net>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH - resend] memblock: Don't adjust size in memblock_find_base()
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On 02/03/2011 12:25 PM, Andrew Morton wrote:
> On Fri, 28 Jan 2011 16:37:47 -0800
> Yinghai Lu <yinghai@kernel.org> wrote:
> 
>>
>> While applying patch to use memblock to find aperture for 64bit x86.
>> Ingo found system with 1g + force_iommu
>>
>>> No AGP bridge found
>>> Node 0: aperture @ 38000000 size 32 MB
>>> Aperture pointing to e820 RAM. Ignoring.
>>> Your BIOS doesn't leave a aperture memory hole
>>> Please enable the IOMMU option in the BIOS setup
>>> This costs you 64 MB of RAM
>>> Cannot allocate aperture memory hole (0,65536K)
> 
> I'm trying to work out if we should backport this fix into earlier
> kernels and as is often the case, I wasn't given enough information.
> 
> What are the end-user visible effects of this?  The kernel cannot use
> the AGP bridge?  64MB of RAM wasted?  Something else?

that is needed for further cleanup memblock with x86.

http://git.kernel.org/?p=linux/kernel/git/tip/linux-2.6-tip.git;a=shortlog;h=refs/heads/x86/bootmem

but it triggers another old bug in core memblock on one Ingo test machine. (with 1g ram but have iommu forced set for debug)
end-user is not supposed to have this conf.

Thanks

Yinghai