Re: [PATCH v3 1/4] x86, kdump: Set crashkernel_low automatically

From: Yinghai Lu
Date: Mon Apr 08 2013 - 14:37:14 EST

On Mon, Apr 8, 2013 at 12:09 AM, Dave Young <dyoung@xxxxxxxxxx> wrote:
>> We have now modified crashkernel=X to allocate memory beyong 4G (if
>> available) and do not allocate low range for crashkernel if the user
>> does not specify that with crashkernel_low=Y. This causes regression
>> if iommu is not enabled. Without iommu, swiotlb needs to be setup in
>> first 4G and there is no low memory available to second kernel.
> Is it possible to reuse the 1st kernel swiotlb region in 2nd capture
> kernel if it's available?

If the first kernel is using intel iommu, and swiotlb is freed after intel
iommus is enabled in first kernel.

>> 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.
> How about make swiotlb size tunable in 1st kernel as well such as adding
> a swiotlb_size= to cmdline, if it's set in 1st kernel crashkernel
> reserving code can take it automaticlly.
can not understand this.


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