[PATCH -V7 09/18] powerpc: Switch 16GB and 16MB explicit hugepages to a different page table format

[David Gibson]

On Mon, Apr 29, 2013 at 01:07:30AM +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com>
> 
> We will be switching PMD_SHIFT to 24 bits to facilitate THP impmenetation.
> With PMD_SHIFT set to 24, we now have 16MB huge pages allocated at PGD level.
> That means with 32 bit process we cannot allocate normal pages at
> all, because we cover the entire address space with one pgd entry. Fix this
> by switching to a new page table format for hugepages. With the new page table
> format for 16GB and 16MB hugepages we won't allocate hugepage directory. Instead
> we encode the PTE information directly at the directory level. This forces 16MB
> hugepage at PMD level. This will also make the page take walk much simpler later
> when we add the THP support.
> 
> With the new table format we have 4 cases for pgds and pmds:
> (1) invalid (all zeroes)
> (2) pointer to next table, as normal; bottom 6 bits == 0
> (3) leaf pte for huge page, bottom two bits != 00
> (4) hugepd pointer, bottom two bits == 00, next 4 bits indicate size
> of table
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>

Mostly ok, except that in several pages your comments imply you have
16M and 16M page directory levels, but you haven't actually made that
change yet.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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