linux-kernel - Re: [PATCH v3] x86, kdump: Set crashkernel

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Date:	Mon, 18 Mar 2013 16:26:57 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	WANG Chao <chaowang@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] x86, kdump: Set crashkernel_low automatically

On Mon, Mar 18, 2013 at 3:52 PM, H. Peter Anvin <hpa@...or.com> wrote:
> On 03/18/2013 02:25 PM, Yinghai Lu wrote:
>> Current code does not set low range for crashkernel if the user
>> does not specify that.
>>
>> That cause regressions on system that does not support intel_iommu
>> properly.
>>
>> Chao said that his system does work well on 3.8 without extra parameter.
>> even iommu does not work with kdump.
>>
>> Set crashkernel_low automatically if the user does not specify that.
>>
>> For system that does support IOMMU with kdump properly, user could
>> specify crashkernel_low=0 to save that 72M low ram.
>>
>> -v3: add swiotlb_size() according to Konrad.
>>
>> Reported-by: WANG Chao <chaowang@...hat.com>
>> Tested-by: WANG Chao <chaowang@...hat.com>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>
> Can we get a bit more of an explanation instead of "and etc 8M"?  At
> least a hint of what kind of objects would go in there...

now only have:
swiotlb overflow buffer

        v_overflow_buffer = alloc_bootmem_low_pages_nopanic(
                                                PAGE_ALIGN(io_tlb_overflow));

and
     /*
      * When the IOMMU overflows we return a fallback buffer. This
sets the size.
     */
     static unsigned long io_tlb_overflow = 32*1024;

so it is 32K, and I round it to 8M.
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