[Crash-utility] [PATCH]Crash-Utility: s390x: Auto-detect the correct MAX_PHYSMEM_BITS used in vmcore being analyzed.

[Mahesh J Salgaonkar]

On 2011-12-21 12:12:54 Wed, Dave Anderson wrote:
> 
> 
> ----- Original Message -----
> > 
> > And complicating matters even further, your patch presumes that the
> > kernel has configured CONFIG_SPARSEMEM_EXTREME in conjunction with
> > CONFIG_SPARSEMEM.  Would it be possible for an s390x to be configured
> > with just CONFIG_SPARSEMEM alone?  If so, your patch breaks down.
> > 
> > Or is there another way you can determine which MAX_PHYSMEM_BITS value
> > is in use?
> > 
> > Dave
> > 
> 
> Using your scheme, this is the best I can come up with (untested):
> 
> --- s390x.c     10 Nov 2011 14:37:15 -0000      1.57
> +++ s390x.c     21 Dec 2011 17:07:20 -0000
> @@ -282,6 +282,43 @@
>         }
>  }
> 
> +static int
> +set_s390x_max_physmem_bits(void)
> +{
> +       int array_len, dimension;
> +
> +       if (!kernel_symbol_exists("mem_section"))
> +               return TRUE;
> +
> +       if (!(array_len = get_array_length("mem_section", &dimension, 0))
> +               return FALSE;
> +

Agree, Makes sense.

> +       /*
> +        * If not CONFIG_SPARSEMEM_EXTREME, presume the older 42.
> +        */
> +       if (dimension) { 
> +               machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_OLD;
> +               return TRUE;
> +       }

Even with max_physmem_bits = 46, it may be possible that newer kernel can be
built with CONFIG_SPARSEMEM and !CONFIG_SPARSEMEM_EXTREME. In which case
dimension can still hold +ve value and we may end up seletecting wrong
value for physmem_bits.

> +
> +       /*
> +        * The older s390x kernels uses _MAX_PHYSMEM_BITS as 42 and the
> +        * newer kernels uses 46 bits.
> +        */
> +       STRUCT_SIZE_INIT(mem_section, "mem_section");
> +       machdep->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;
> +
> +       machdep->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;
> +}
> +

The above code does compare array_len for both the conditions
CONFIG_SPARSEMEM_EXTREME and !CONFIG_SPARSEMEM_EXTREME for old/new
max_physmem_bits. However, with use of dimension value the above
logic can be more simpler like this:

diff --git a/s390x.c b/s390x.c
index 22e29a9..5b6a38e 100755
--- a/s390x.c
+++ b/s390x.c
@@ -282,6 +282,53 @@ static void s390x_process_elf_notes(void *note_ptr, unsigned long size_note)
 	}
 }
 
+static int
+set_s390x_max_physmem_bits(void)
+{
+	int array_len, dimension;
+
+	if (!kernel_symbol_exists("mem_section"))
+		return TRUE;
+
+	if (!(array_len = get_array_length("mem_section", &dimension, 0)))
+		return FALSE;
+
+	/*
+	 * The older s390x kernels uses _MAX_PHYSMEM_BITS as 42 and the
+	 * newer kernels uses 46 bits.
+	 */
+
+	STRUCT_SIZE_INIT(mem_section, "mem_section");
+
+	/*
+	 * !CONFIG_SPARSEMEM_EXTREME
+	 */
+	if (dimension) {
+		machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_OLD;
+		if (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT()))
+			return TRUE;
+
+		machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_NEW;
+		if (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT()))
+			return TRUE;
+
+		return FALSE;
+	}
+
+	/*
+	 * CONFIG_SPARSEMEM_EXTREME
+	 */
+	machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_OLD;
+	if (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
+			return TRUE;
+
+	machdep->max_physmem_bits = _MAX_PHYSMEM_BITS_NEW;
+	if (array_len == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME()))
+		return TRUE;
+
+	return FALSE;
+}
+
 /*
  *  Do all necessary machine-specific setup here.  This is called several
  *  times during initialization.


What do you think?

Thanks,
-Mahesh.

-- 
Mahesh J Salgaonkar