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SubjectRe: [PATCH 0/8] De-couple sysfs memory directories from memory sections
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On Wed, 2010-09-22 at 13:40 -0500, Nathan Fontenot wrote:
> On 09/22/2010 10:20 AM, Dave Hansen wrote:
> > and phys_index's calculation needs to be:
> >
> > mem->start_phys_index * SECTION_SIZE / memory_block_size_bytes()
>
> I'm not sure if I follow where you suggest using this formula. Is this
> instead of what is used now, the base_memory_block_id() calculation?
>
> If so, then I'm not sure it would work. The formula used in base_memory_block_id()
> is done because the memory sections are not guaranteed to be added to the
> memory block starting with the first section of the block.
>
> If you meant somewhere else let me know.

My point was just that if we change the "block_size_bytes" contents,
then we have to scale down the "memoryXXXX/phys_index" by that same
amount.
It *used* to be in numbers of SECTION_SIZE units, and I think it still
is:

- mem->start_phys_index = __section_nr(section);
+ mem->start_phys_index = base_memory_block_id(__section_nr(section));
+ mem->end_phys_index = mem->start_phys_index + sections_per_block - 1;

but now it needs to be changed to be in memory_block_size_bytes() units,
*NOT* SECTION_SIZE units.

Let's say we have a system with 4 16MB sections starting at 0x0.
Before, we would have:

block_size_bytes: 16777216
memory0/phys_index: 0
memory1/phys_index: 1
memory2/phys_index: 2
memory3/phys_index: 3

Now, we change memory_block_size_bytes() to be 32MB instead. We reduce
the number of sections in half, and I think the right thing to get is:

block_size_bytes: 33554432
memory0/phys_index: 0
memory1/phys_index: 1

I think, with your code (as it stands in these patches, no fixes) that
we'd instead get this:

block_size_bytes: 16777216
memory0/phys_index: 0
memory1/phys_index: 2

Without consulting "end_phys_index" (which isn't and can't be a part of
the existing ABI), we'd think that we have two 16MB banks instead of
four.


-- Dave



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