Re: [PATCH 1/2 v2] x86: add max_addr boot option

Kamezawa Hiroyuki
2012-06-13T05:23:03Z

(2012/06/13 12:29), H. Peter Anvin wrote:
> On 06/12/2012 07:21 PM, Kamezawa Hiroyuki wrote:
>>
>> But now, we know mem= boot option is buggy....it acts as max_addr=
>> option, we have concerns that 'someone may fix mem= option as sane as ia64. because
>> it's buggy".
>>
>> We'd like to fix mem= boot option by ourselves and preserve old behavior
>> with max_addr= boot option, which ia64 has.
>>
>
> Now I'm *really* confused.
>
> Realistically, there is no point in the old mem= behavior of assuming a
> contiguous chunk of memory up to that point; it simply doesn't match how
> modern hardware is constructed. Your notion that ia64 is "sane" is
> probably more of "outdated" in my opinion.
>
> As such, the current behavior for mem= seems like the right thing and
> the change was intentional (not to mention has been in place since
> kernel 2.5.65, back in 2003); it also solves your requirements. If you
> are concerned about it, it would make more sense to make sure it is
> documented as intentional.
>
> In fact, it looks like IA64 introduced a divergence when the max_addr=
> patch was introduced in 2004. You're basically proposing the same
> divergence for x86 now; talk about having the tail wag the dog.
>
> Sorry. NAK.
>

Hmm, them, it's ok to post a patch for fixing kernel-param

mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
Amount of memory to be used when the kernel is not able
to see the whole system memory or for test.
[X86-32] Use together with memmap= to avoid physical
address space collisions. Without memmap= PCI devices
could be placed at addresses belonging to unused RAM.

to explain 'work as limiting max address' and implementing current mem= behavior
in x86-64/efi code ?

Thanks,
-Kame