On 09/22/2010 10:20 AM, Dave Hansen wrote:

On Wed, 2010-09-22 at 09:15 -0500, Nathan Fontenot wrote:

quoted

For architectures that define their own version of this routine,
as is done for powerpc in this patchset, the view in userspace
would change such that each memoryXXX directory would span
multiple memory sections.  The number of sections spanned would
depend on the value reported by memory_block_size_bytes.

In both cases a new file 'end_phys_index' is created in each
memoryXXX directory.  This file will contain the physical id
of the last memory section covered by the sysfs directory.  For
the default case, the value in 'end_phys_index' will be the same
as in the existing 'phys_index' file.

Hi Nathan,

There's one bit missing here, I think.

"block_size_bytes" today means two things today:
1. the SECTION_SIZE from sparsemem
2. the size covered by each memoryXXXX directory

SECTION_SIZE isn't exposed to userspace, but the memoryXXXX directories
are.  You've done all of the heavy lifting here to make sure that the
memory directories are no longer bound to SECTION_SIZE, but you've also
broken the assumption that _each_ directory covers "block_size_bytes".

I think it's fairly simple to fix.  block_size_bytes() needs to return
memory_block_size_bytes(),

yes, missed that.  I will update the patch set to include this.

                           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.

-Nathan

That way, to userspace, it just looks like before, but with a larger
SECTION_SIZE.  Doing that preserves the ABI pretty nicely, I believe.

-- Dave