[v3,2/3] powerpc: get hugetlbpage handling more generic

[Scott Wood]

On Wed, Sep 21, 2016 at 10:11:54AM +0200, Christophe Leroy wrote:
> Today there are two implementations of hugetlbpages which are managed
> by exclusive #ifdefs:
> * FSL_BOOKE: several directory entries points to the same single hugepage
> * BOOK3S: one upper level directory entry points to a table of hugepages
> 
> In preparation of implementation of hugepage support on the 8xx, we
> need a mix of the two above solutions, because the 8xx needs both cases
> depending on the size of pages:
> * In 4k page size mode, each PGD entry covers a 4M bytes area. It means
> that 2 PGD entries will be necessary to cover an 8M hugepage while a
> single PGD entry will cover 8x 512k hugepages.
> * In 16 page size mode, each PGD entry covers a 64M bytes area. It means
> that 8x 8M hugepages will be covered by one PGD entry and 64x 512k
> hugepages will be covers by one PGD entry.
> 
> This patch:
> * removes #ifdefs in favor of if/else based on the range sizes
> * merges the two huge_pte_alloc() functions as they are pretty similar
> * merges the two hugetlbpage_init() functions as they are pretty similar
> 
> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>

With this patch on e6500, running the hugetlb testsuite results in the
system hanging in a storm of OOM killer invocations (I'll try to debug
more deeply later).  This patch also changes the default hugepage size on
FSL book3e from 4M to 16M.

-Scott