On 04/11/2013 07:55 AM, Yinghai Lu wrote: > On Thu, Apr 11, 2013 at 5:26 AM, Thomas Renninger <trenn at suse.de> wrote: >> Currently ranges are passed via kernel boot parameters: >> memmap=exactmap memmap=X#Y memmap= >> >> Pass them via e820 table directly instead. > > how to address "saved_max_pfn" referring in kernel? > > kernel need to use saved_max_pfn from old e820 in > drivers/char/mem.c::read_oldmem() > > mips and powerpc they are passing that from command line "savemaxmem=" > > x86 should use that too? > Oh bloody hell, yet another f-ing "max_pfn" variable. The *only* one that makes any kind of sense is max_low_pfn (marking the cutoff to highmem)... the pretty much the rest of them are just plain wrong. And I don't mean "mildly annoying", I mean "catastrophically wrong semantics". In this case, it introduces a completely arbitrary distinction between a nonmemory range below a high water mark and a nonmemory range above that high water mark. In fact, from reading the code it seems pretty clear that the device will blindly assume that anything below saved_max_pfn is memory and will try to map it cachable... which will #MC on quite a few machines. This kind of crap HAS TO STOP. Memory is discontiguous, deal with it and deal with it properly. I also have to admit that I don't see the difference between /dev/mem and /dev/oldmem, as the former allows access to memory ranges outside the ones used by the current kernel, which is what the oldmem device seems to be intended to od. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.
