Re: [PATCH 0/3] Cleanup kdump memmap= passing and e820 usage

Eric W. Biederman
2013-01-30T22:29:24Z

"H. Peter Anvin" <hpa@zytor.com> writes:

> On 01/30/2013 01:57 PM, Eric W. Biederman wrote:
>>>
>>> Yes, those seem to be the options, and we're currently discussing which one.
>>>
>>> The second seems to make more sense to me. The kexec tools build the
>>> memory map anyway, and it makes sense to me at least to just build a
>>> memory map with the appropriate regions marked as a dumpable type.
>>
>> This dumpable type doesn't make sense to me. Are you suggesting making
>> regions that are memory but that we should not use a special memory
>> type?
>
> Yes.
>
>> I think I would prefer that to call that new type RESERVED_MEM or
>> RESERVED_CACHABLE. Being more specific is fine but dumpable certainly
>> doesn't bring to mind what we are saying. Especially since we already
>> communicate which areas were memory to the last kernel in an
>> architecture generic format.
>
> I was thinking that marking them differently might help debugging, at
> least, but yes, we can have a RESERVED_MEM type.
>
> However, Thomas does have a point that the current use of fairly small
> positive values for Linux-defined types is a bad idea. We should use
> negative types, or at least something north of 0x40000000 or so.

Yes. It doesn't much matter in the kernel but when it because part of
the ABI it is a real issue.

Since old kernels treat any value they don't understand as reserved
passing a modified e820 map seems reasonable to me once we have reserved
a special linux value for it.

Eric