On Fri, Jan 21, 2011 at 2:20 AM, Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> wrote:
> On Thu, 2011-01-20 at 18:45 +0900, KyongHo Cho wrote:
>> Sparsemem allows that a bank of memory spans over several adjacent
>> sections if the start address and the end address of the bank
>> belong to different sections.
>> When gathering statictics of physical memory in mem_init() and
>> show_mem(), this possiblity was not considered.
>>
>> This patch guarantees that simple increasing the pointer to page
>> descriptors does not exceed the boundary of a section
> ...
>> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
>> index 57c4c5c..6ccecbe 100644
>> --- a/arch/arm/mm/init.c
>> +++ b/arch/arm/mm/init.c
>> @@ -93,24 +93,38 @@ void show_mem(void)
>>
>> pfn1 = bank_pfn_start(bank);
>> pfn2 = bank_pfn_end(bank);
>> -
>> +#ifndef CONFIG_SPARSEMEM
>> page = pfn_to_page(pfn1);
>> end = pfn_to_page(pfn2 - 1) + 1;
>> -
>> +#else
>> + pfn2--;
>> do {
>> - total++;
>> - if (PageReserved(page))
>> - reserved++;
>> - else if (PageSwapCache(page))
>> - cached++;
>> - else if (PageSlab(page))
>> - slab++;
>> - else if (!page_count(page))
>> - free++;
>> - else
>> - shared += page_count(page) - 1;
>> - page++;
>> - } while (page < end);
>> + page = pfn_to_page(pfn1);
>> + if (pfn_to_section_nr(pfn1) < pfn_to_section_nr(pfn2)) {
>> + pfn1 += PAGES_PER_SECTION;
>> + pfn1 &= PAGE_SECTION_MASK;
>> + } else {
>> + pfn1 = pfn2;
>> + }
>> + end = pfn_to_page(pfn1) + 1;
>> +#endif
>
> This problem actually exists without sparsemem, too. Discontigmem (at
> least) does it as well.
>
Actually, as long as a bank in meminfo only resides in a pgdat, no
problem happens
because there is no restriction of size of area in a pgdat.
That's why I just considered about sparsemem.
> The x86 version of show_mem() actually manages to do this without any
> #ifdefs, and works for a ton of configuration options. It uses
> pfn_valid() to tell whether it can touch a given pfn.
>
> Long-term, it might be a good idea to convert arm's show_mem() over to
> use pgdat's like everything else. But, for now, you should just be able
> to do something roughly like this:
>
> - page = pfn_to_page(pfn1);
> - end = pfn_to_page(pfn2 - 1) + 1;
> -
> - do {
> + for (pfn = pfn1; pfn < pfn2; pfn++) {
> + if (!pfn_valid(pfn))
> + continue;
> + page = pfn_to_page(pfn);
> +
> total++;
> if (PageReserved(page))
> reserved++;
> else if (PageSwapCache(page))
> cached++;
> else if (PageSlab(page))
> slab++;
> else if (!page_count(page))
> free++;
> else
> shared += page_count(page) - 1;
> page++;
> - } while (page < end);
> + }
>
> That should work for sparsemem, or any other crazy memory models that we
> come up with. pfn_to_page() is pretty quick, especially when doing it
> in a tight loop like that.
>
That's true.
I worried that pfn_to_page() in sparsemem is a bit slower than that in flatmem.
Moreover, the previous one didn't use pfn_to_page() but page++ for the
performance.
Nevertheless, I also think that pfn_to_page() make the code neat.
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