On Tue, Jan 22, 2019 at 05:27:29PM -0800, Dan Williams wrote:
>On Mon, Jan 21, 2019 at 6:49 PM Wei Yang <richardw.y...@linux.intel.com> wrote:
>>
>> There are two places to calculate npfns in nd_pfn_init(), while they use
>> difference size to calculate.
>>
>> Use PAGE_SIZE would be more proper for calculation.
>
>No, this would make the kernel have different output based on
>PAGE_SIZE. It should be possible for a PAGE_SIZE==64K system to create
>a valid info-block for PAGE_SIZE==4K system. This would need to encode
>the PAGE_SIZE in the info-block if it were to ever support non-4K
>PAGE_SIZE systems.
>
I am confused.
Generally, npfns is used in two functions: nd_pfn_init() and
__nvdimm_setup_pfn().
The code flow looks like this:
nvdimm_setup_pfn()
nd_pfn_init()
npfns = SECTION_ALIGN(trim_size / PAGE_SIZE)
offset = start + npfns * page_struct
npfns = (trim_size - offset) / SZ_4K
pfn_sb->npfns
__nvdimm_setup_pfn()
nd_pfn->npfns = pfn_sb->npfns
or
nd_pfn->npfns = (trim_size - offset) / PAGE_SIZE
My questions are:
1. offset = start + npfns * page_struct
This means the number of page struct we reserve in meta-data area is
calculated with PAGE_SIZE page.
But we set pfn_sb->npfns = (trim_size - offset) / SZ_4K, which
means we tell hardware the number of pages is calculated with 4K size.
Would this be a conflict? Or at least we need to reserve more meta-data
area to hold page struct?
2. When mode == PFN_MODE_PMEM and PAGE_SIZE == 64K,
nd_pfn->pfn_sb->npfns is sure to be bigger than nd_pfn->npfns. Because
nd_pfn->pfn_sb->npfns = (trim_size - offset) / 4K
nd_pfn->npfns = (trim_size - offset) / 64K
If we are sure for the final result, why we would like to have this
calculation again?
>Another consideration is that a PAGE_SIZE==4K infoblock is compatible
>with a PAGE_SIZE==64K system. All that happens is that the memmap
>reserve area is oversized and portions go unused. The reverse is not
>true.
The oversized memap reserve area is SECTION size aligned? If so, it looks we
took that into consideration when we calculate offset.
--
Wei Yang
Help you, Help me
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