[Crash-utility] ARM support for CONFIG_SPARSEMEM: (was Re: DDimage)

[takuo.koguchi.sw at hitachi.com]

Thanks Dave, MW, Jan,

I tried the patch which set machdep->section_size_bits and machdep->max_physmem_bits.

When _SECTION_SIZE_BITS is 28, I got the following error, and failed in sparse_mem_init()
PAGESIZE=4096
mem_section_size = 0
NR_SECTION_ROOTS = 0
NR_MEM_SECTIONS = 16
SECTIONS_PER_ROOT = 512
SECTION_ROOT_MASK = 0x1ff
PAGES_PER_SECTION = 65536
crash: invalid size request: 0  type: "memory section root table"


And when _SECTION_SIZE_BITS is 22, I got the following and sparse_mem_init() returns with out error.

PAGESIZE=4096
mem_section_size = 8
NR_SECTION_ROOTS = 2
NR_MEM_SECTIONS = 1024
SECTIONS_PER_ROOT = 512
SECTION_ROOT_MASK = 0x1ff
PAGES_PER_SECTION = 1024

... But I got another error later, which I will report later.


In memory.c:sparse_mem_init(),
 vt->mem_sec is malloced as mem_section_size bytes block and readmem is called.
I suppose the mem_section_size should not be zero.  I do not know _SECTION_SIZE_BITS 22 is correct or not,
but the following caliculation of NR_SECTION_ROOTS() looks suspicious to me.
#define NR_SECTION_ROOTS()	(NR_MEM_SECTIONS() / SECTIONS_PER_ROOT())

Something like (((NR_MEM_SECTIONS() - 1)/ SECTIONS_PER_ROOT()) + 1) ?


Best Regard,

Takuo 



>[ dropped my Nokia address from the CC list, since I'm not working for Nokia
>  anymore ]
>
>On Tue, May 24, 2011 at 09:58:48AM -0400, Dave Anderson wrote:
>> 
>> BTW, I await any patches from the ARM folks to set these bits
>> appropriately.  Currently there is this for ARM in defs.h:
>> 
>>   #ifdef ARM
>>   ... [ cut ] ...
>> 
>>   #define _SECTION_SIZE_BITS      28
>>   #define _MAX_PHYSMEM_BITS       32
>> 
>>   #endif  /* ARM */
>> 
>> Yet you state above that you're using 22 for _SECTION_SIZE_BITS.
>
>This varies between different SoCs and it is not used by others. Since it is
>not stored in a crashdump IIRC, we really cannot set that value dynamically.
>
>So I see two options:
>
>	1) leave it as is and make crash to complain when it detects such
>	   situation or
>	2) guess the values and try to do the right thing (TM)
>
>My preference goes with 2) provided that we can get it working on majority of
>the ARM SoCs.
>
>We could try to stick with _SECTION_SIZE_BITS=28, as it seems to be largest
>currently used section size amongst different ARM SoCs, and hope that it works
>with others where this is smaller.
>
>Jan, Takuo: maybe you could try whether following patch works? I don't have
>any hardware which use SPARSEMEM so I'm unable to test it.
>
>Regards,
>MW
>
>diff --git a/arm.c b/arm.c
>index 0347166..9d4afcc 100644
>--- a/arm.c
>+++ b/arm.c
>@@ -260,6 +260,9 @@ arm_init(int when)
> 		    STRUCT_EXISTS("pteval_t"))
> 			machdep->flags |= PGTABLE_V2;
> 
>+		machdep->section_size_bits = _SECTION_SIZE_BITS;
>+		machdep->max_physmem_bits = _MAX_PHYSMEM_BITS;
>+
> 		if (symbol_exists("irq_desc"))
> 			ARRAY_LENGTH_INIT(machdep->nr_irqs, irq_desc,
> 					  "irq_desc", NULL, 0);
>
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