[PATCH] makedumpfile: s390x: Auto-detect the correct MAX_PHYSMEM_BITSused in vmcore being analyzed.

[tachibana at mxm.nes.nec.co.jp]

Hi Mahesh,

Thank you for the patch.
I will review it.
However I have never dumped 1 terabyte or more data using makedumpfile.
Has anyone ever dumped it successfully?

Thanks.
tachibana

On 2011/12/20 16:06:01 +0530, Mahesh J Salgaonkar <mahesh at linux.vnet.ibm.com> wrote:
> Hi Tachibana,
> 
> As part of the s390 patch to add support for > 4TB system memory (present in
> linux-next tree), the newer s390 kernel will bump the MAX_PHYSMEM_BITS from
> 42 to 46. Once that patch makes into umpstream kernel, this change will need
> to go into makedumpfile.  For now, I am posting this patch for a review.
> 
> Reference: http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commit;h=8980036860565a6d2a4f95bb097927e832
fa3d1a
> 
> Thanks,
> -Mahesh.
> 
> 
> From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
> 
> So far s390x kernel was using 42 bits for MAX_PHYSMEM_BITS that use to
> support maximum of 4TB of memory. In order to support bigger systems,
> the newer s390x kernel will now use 46 bits for MAX_PHYSMEM_BITS to support
> maximum of 64TB of memory.
> 
> This patch auto-detects the correct value to use for MAX_PHYSMEM_BITS by
> examining the mem_section array size from the vmcore being analyzed.
> 
> Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
> ---
>  arch/s390x.c   |   27 ++++++++++++++++++++++++++-
>  makedumpfile.h |    3 ++-
>  2 files changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390x.c b/arch/s390x.c
> index 9237eaa..c73220a 100644
> --- a/arch/s390x.c
> +++ b/arch/s390x.c
> @@ -60,6 +60,28 @@
>  #define pte_offset(x)		(pte_index(x) * sizeof(unsigned long))
>  
>  int
> +set_s390x_max_physmem_bits(void)
> +{
> +	long array_len = ARRAY_LENGTH(mem_section);
> +	/*
> +	 * The older s390x kernels uses _MAX_PHYSMEM_BITS as 42 and the
> +	 * newer kernels uses 46 bits.
> +	 */
> +
> +	info->max_physmem_bits  = _MAX_PHYSMEM_BITS_OLD;
> +	if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> +		|| (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> +		return TRUE;
> +
> +	info->max_physmem_bits  = _MAX_PHYSMEM_BITS_NEW;
> +	if ((array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
> +		|| (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT())))
> +		return TRUE;
> +
> +	return FALSE;
> +}
> +
> +int
>  get_machdep_info_s390x(void)
>  {
>  	unsigned long vmalloc_start;
> @@ -70,7 +92,10 @@ get_machdep_info_s390x(void)
>  		flag_ignore_r_char = 1;
>  
>  	info->section_size_bits = _SECTION_SIZE_BITS;
> -	info->max_physmem_bits  = _MAX_PHYSMEM_BITS;
> +	if (!set_s390x_max_physmem_bits()) {
> +		ERRMSG("Can't detect max_physmem_bits.\n");
> +		return FALSE;
> +	}
>  	info->page_offset = __PAGE_OFFSET;
>  
>  	if (SYMBOL(_stext) == NOT_FOUND_SYMBOL) {
> diff --git a/makedumpfile.h b/makedumpfile.h
> index b3de521..a95d132 100644
> --- a/makedumpfile.h
> +++ b/makedumpfile.h
> @@ -531,7 +531,8 @@ do { \
>  #define KERNELBASE		(0)
>  #define KVBASE			KERNELBASE
>  #define _SECTION_SIZE_BITS	(28)
> -#define _MAX_PHYSMEM_BITS	(42)
> +#define _MAX_PHYSMEM_BITS_OLD	(42)
> +#define _MAX_PHYSMEM_BITS_NEW	(46)
>  
>  /* Bits in the segment/region table address-space-control-element */
>  #define _ASCE_TYPE_MASK		0x0c
>