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    SubjectRe: [PATCH 1/2 v2] x86: add max_addr boot option
    At 06/13/2012 11:29 AM, H. Peter Anvin Wrote:
    > On 06/12/2012 07:21 PM, Kamezawa Hiroyuki wrote:
    >> But now, we know mem= boot option is 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 probably more of "outdated" in my opinion.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.

    Here is the document(Documentation/kernel-parameters.txt):

    mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory

    The implementation of mem= on ia64 is the same as the description in the document, but
    the implementation of mem= on x86 box is not the same as the descrition.

    Now, which should we fix? Document or the implementition?

    Another problem is: the mem= cannot work if the user specifies add_efi_memmap
    option. I think we should also fix this problem.

    Wen Congyang
    > 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.
    > -hpa

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