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

[Dave Young <dyoung@redhat.com>]

On 04/09/2013 02:37 AM, Yinghai Lu wrote:
> On Mon, Apr 8, 2013 at 12:09 AM, Dave Young <dyoung@redhat.com> 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.

Ok, also it's hard to handle such as 1st kernel iommu=off, 2nd kernel
iommu=on etc.

I have another question, under x86_64 consider 1st kernel memory < 4G,
is the swiotlb memory still necessary?

> 
>>
>>>
>>> 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.

This maybe out of topic. I means swiotlb size is hardcoded, I'm thinking
how about make it configurable via kconfig or boot cmdline.

> 
> Thanks
> 
> Yinghai
> 


-- 
Thanks
Dave