>>>> Did you mean the patch below is wrong?
>>>>
>>>> commit 1e93ee75f9d47c219e833210eb31e4a747cc3a8d
>>>> Author: Mika Westerberg <ext-mika.1.westerberg at nokia.com>
>>>> Date: Tue Jun 22 09:59:10 2010 +0300
>>>>
>>>> use ARCH_PFN_OFFSET for pfn_to_paddr/paddr_to_pfn translations
>>>>
>>>> Your description sounds we should fix the way to convert paddr to pfn,
>>>> but there is no such fix in your patch.
>>>
>>>
>>> Yes, my first version does just as what you say. But the patch is huge.
>>> I thing this patch is much better.
>>>
>>> Though commit 1e93ee75f9d47c219e833210eb31e4a747cc3a8d brings some problems
>>> . But we can easy fix them.
>>>
>>>
>>> Make my platform for example: 80000 sparse memory model.
>>> mem 1G ; SECTION_SIZE_BITS 26
>>>
>>> (a) for the kernel
>>>
>>> section number |phy start | start pfn | end pfn | valid | mem_section |
>>> 0 |0 | 0 | 3fff | 0 | [0] |
>>> 1 |4000000 | 4000 | 7fff | 0 | [1] |
>>> 2 |8000000 | 8000 | bfff | 0 | [2] |
>>>
>>> [cut ...]
>>>
>>> 32 |80000000 | 80000 | 83fff | 1 | [32] |
>>> 33 |84000000 | 84000 | 87fff | 1 | [33] |
>>>
>>> [cut ...]
>>>
>>> 47 |bfc00000 | bfc000 | bffff | 1 | [47] |
>>>
>>>
>>> (b) for makedumpfile
>>>
>>>
>>> 0 |80000000 | 0 | 3fff | 0 | [0] |
>>> 1 |84000000 | 4000 | 7fff | 0 | [1] |
>>>
>>> [cut ...]
>>>
>>> 15 |bfc00000 | 3c000 | 3ffff | 1 | [15] |
>>>
>>>
>>> So makedumpfile removes the offset of section number and pfn. The relationship between
>>> pfn and section number remains as before. So this will not introduce problem.
>>>
>>> But the section nember and mem_section array do not match each other.
>>>
>>> For paddr 80000000
>>> kernel : pfn 8000: mem_section: 32
>>> makedumpfile : pfn 0 : mem_section: 0
>>>
>>> And we do not remove the offset of array mem_section. So makedumofile can not
>>> get the right page struct. When fix this offset, everything is ok.
>>
>> Thanks for your explanation, I understand the sparse_mem case.
>>
>>> But If we revert 1e93ee75f9d:
>>>
>>> (a) codes likes "for(pfn = 0" ,"for_each_cycle(0" and "for (section_nr = 0" should be changed;
>>> (b) Due to "set_bit_on_1st_bitmap(pfn, cycle)", we will waste some bits.
>>> (c) crash utility should also be changed.
>>>
>>> BTW, when ARCH_PFN_OFFSET=0, section nember and mem_section matches each other..
>>> So no problem was intrduced
>>>
>>>>
>>>>> For the cases of ARCH_PFN_OFFSET=0 or non sparse memormy model,
>>>>> this introduces no problem.
>>>>>
>>>>> But for my arma9 platform with ARCH_PFN_OFFSET=0x80000 and sparse
>>>>> memory model. Makedumfile can not get the mem_map correctly. It it
>>>>> due to there is still offset for mem_map array.
>>>>
>>>> Why the other memory models are OK? There is no offset even if ARCH_PFN_OFFSET!=0?
>>>> I need more explanation to understand this issue.
>>>
>>> (1) For flatmem, the mem_map is continuous, And the start address of mem_map comes from
>>> the kernel symbol.
>>>
>>> For paddr 80000000
>>> kernel : pfn 8000: mem_map[0]
>>> makedumpfile : pfn 0 : mem_map[0]
>>>
>>> This will not introduce problem.
>>
>> I understand that alloc_node_mem_map() allocates mem_map for flatmem and it
>> considers ARCH_PFN_OFFSET like:
>>
>> if (pgdat == NODE_DATA(0)) {
>> mem_map = NODE_DATA(0)->node_mem_map;
>> #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
>> if (page_to_pfn(mem_map) != pgdat->node_start_pfn)
>> mem_map -= (pgdat->node_start_pfn - ARCH_PFN_OFFSET);
>> #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
>
>In all cases, mem_map indicates the start address of the mem_map.
>
>I think this is the inner process for the kernel, which we should not consider. Because once
>we get the mem_map symbol value and the maxpfn from the vmcore. We know the start and length
>of mem_map. And we can get every page struct correctly.
>
>For makedumpfile:
>
> get_mm_flatmem(void)
>{
> ....
>2409 if (!readmem(VADDR, SYMBOL(mem_map), &mem_map, sizeof mem_map)//get the mem_map value
> ....
>2421 if (is_xen_memory())
>2422 dump_mem_map(0, info->dom0_mapnr, mem_map, 0);
>2423 else
>2424 dump_mem_map(0, info->max_mapnr, mem_map, 0);
>
>}
>
>So for flat memory model, makedumpfile can always get the correct mem_map.
I don't worry that we can't get the start address of the mem_map.
You said the kernel doesn't consider ARCH_PFN_OFFSET when converting paddr
to pfn, this sounds the kernel doesn't make an exception for the pages lower
than ARCH_PFN_OFFSET in page management to me.
I mean I worry about a situation like below:
(For example, ARCH_PFN_OFFSET=0x4)
phys addr | pfn for | pfn for | valid | mem_map
| kernel | makedumpfile | |(struct page)
--------------+--------------+----------------+---------+------------
0 - fff | 0 | X | 0 | [0]
1000 - 1fff | 1 | X | 0 | [1]
2000 - 2fff | 2 | X | 0 | [2]
3000 - 3fff | 3 | X | 0 | [3]
4000 - 4fff | 4 | 0 | 1 | [4]
5000 - 5fff | 5 | 1 | 1 | [5]
6000 - 6fff | 6 | 2 | 1 | [6]
...
When we check the page flag of the page[4000-4fff] in makedumpfile, we
have to read mem_map[4], but makedumpfile reads mem_map[0] due to
paddr_to_pfn(). This is my worry.
Actually, the similar gap exists in the sparse_mem case as you described,
so I suspect we have to take care of it also for other memory models.
>> }
>>
>> So there is no problem in this model since the top of mem_map corresponds to
>> ARCH_PFN_OFFSET, right?
>
>I don't think so. Is it clear for my words above?
>
>>
>>> (2) For discontigmem, it manages the mem_map with node_memblk. commit
>>> 1e93ee75f9d47c21 also does no harm.
>>
>> alloc_node_mem_map() allocates mem_map also for discontigmem, but I can't find
>> any codes to consider ARCH_PFN_OFFSET for this model.
>> So I suspect the mismatch between the pfn for makedumpfile and the actual content
>> of mem_map can exist. Could you explain why this case is OK in more detail?
>>
>Actually I did not test this memory model. I reach my conclusion via the codes.
>
>get_mm_discontigmem
>{
>....
>for (i = 0; i < vt.numnodes; i++) { //loop for every node
>2591 if (!readmem(VADDR, pgdat + OFFSET(pglist_data.node_start_pfn),
>2592 &pfn_start, sizeof pfn_start)) { //get pfn_start for this node
>....
>2596 if (!readmem(VADDR,pgdat+OFFSET(pglist_data.node_spanned_pages),
>2597 &node_spanned_pages, sizeof node_spanned_pages)) { //get the number of pages in this node
>
>2603 if (SYMBOL(vmem_map) == NOT_FOUND_SYMBOL) {
>2604 if (!readmem(VADDR, pgdat + OFFSET(pglist_data.node_mem_map), //get the mem_map for this
>node.
>2605 &mem_map, sizeof mem_map)) {
>2606 ERRMSG("Can't get mem_map.\n");
>2607 return FALSE;
>2608 }
>2609 } else
>2610 mem_map = vmem_map + (SIZE(page) * pfn_start);
>....
>}
>
>So I think for discontigmem, makedumpfile can get the start address and length of mem_map from vmcore directly.
>And Everything can go well without ARCH_PFN_OFFSET.
The same can be said, is it not needed to consider ARCH_PFN_OFFSET
to get a page struct from the mem_map?
Thanks
Atsushi Kumagai
>
>Perhaps I need some tests on discontigmem. Did I explan my idea clearly?
>
>
>
>>
>> Thanks
>> Atsushi Kumagai
>>
>>> What do you think?
>>>
>>> Thanks,
>>> Liu Hua
