[Crash-utility] Re: [PATCH] CONFIG_SPARSEMEM for s390(x)

Michael Holzheu wrote: Hi Michael, Actually, the originator of CONFIG_SPARSEMENT support is your IBM compatriot, and can probably answer this best: 4.0-2.22 - Incorporated initial patch-set to implement support for kernels built with CONFIG_SPARSEMEM. (dwilder(a)us.ibm.com) ... Dave is still listed as a member of this mailing list. Anyway, as I understand it, the _MAX_PHYSMEM_BITS() macro for each architecture is a clone of the kernel's per-arch MAX_PHYSMEM_BITS #define. For the s390 arch, it's found in "include/asm-s390/sparsemem.h": #ifndef _ASM_S390_SPARSEMEM_H #define _ASM_S390_SPARSEMEM_H #define SECTION_SIZE_BITS 25 #ifdef CONFIG_64BIT #define MAX_PHYSADDR_BITS 42 #define MAX_PHYSMEM_BITS 42 #else #define MAX_PHYSADDR_BITS 31 #define MAX_PHYSMEM_BITS 31 #endif /* CONFIG_64BIT */ #endif /* _ASM_S390_SPARSEMEM_H */ And it -- along with SECTION_SIZE_BITS -- fits into the math for the SECTIONS_SHIFT value in "include/linux/mmzone.h": SECTIONS_SHIFT 839 #define SECTIONS_SHIFT (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS) And so the crash utility follows its lead: #define SECTION_SIZE_BITS() (machdep->section_size_bits) #define MAX_PHYSMEM_BITS() (machdep->max_physmem_bits) #define SECTIONS_SHIFT() (MAX_PHYSMEM_BITS() - SECTION_SIZE_BITS()) and also using the arch-specific SECTION_SIZE_BITS() in the same manner. So I'm surprised that your patch "works"? It would seem that it would need to: (1) to use "42" for the s390x _MAX_PHYSMEM_BITS, and (2) you would also need to #define a _SECTION_SIZE_BITS value for the two architectures as well. Dave