Re: [Patch 1/7] x86: add CONFIG_KEXEC_AUTO_RESERVE

[Amerigo Wang <amwang@redhat.com>]

Andi Kleen wrote:
> Amerigo Wang <amwang@redhat.com> writes:
>
>   
>> Introduce a new config option KEXEC_AUTO_RESERVE for x86.
>>     
>
> The description of the feature belongs in the changelog.
>
> I like the basic idea, but:
>
>   
>> +config KEXEC_AUTO_RESERVE
>> +	bool "automatically reserve memory for kexec kernel"
>> +	depends on KEXEC
>> +	default y
>> +	---help---
>> +	  Automatically reserve memory for a kexec kernel, so that you don't
>> +	  need to specify numbers for the "crashkernel=X@Y" boot option,
>> +	  instead you can use "crashkernel=auto".
>> +	  On x86, 128M is reserved.
>>     
>
> The obvious problem is the hardcoded 128MB (and 128MB is very large
> for a crash kernel anyways)
>   


I think that size has to be hardcoded, or we can make it a bit 
changeable,  according to the page size.... e.g. on PPC and IA64, page 
size can be 16K or more, but x86's page size is always 4K I think.

Hmm, yes, I choose such a large size in order to be safe, but since you 
feel this is too large, how about 64M on x86? (On x86_64 Fedora and 
RHEL, the size of a kernel binary is about 2M~3M.)
> More useful would seem a crashkernel=size@auto
>   
We already have this, just use "crashkernel=size@0". :)

Thanks.