powerpc/THP: Enable THP on PPC64

We enable only if the we support 16MB page size.

Reviewed-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

2 files changed, 30 insertions, 2 deletions

diff --git a/arch/powerpc/include/asm/pgtable-ppc64.h b/arch/powerpc/include/asm/pgtable-ppc64.h
index e71bd25d62d7..46db09414a10 100644
--- a/arch/powerpc/include/asm/pgtable-ppc64.h
+++ b/arch/powerpc/include/asm/pgtable-ppc64.h
@@ -444,8 +444,7 @@ static inline int pmd_trans_splitting(pmd_t pmd)
         return 0;
 }
 
-/* We will enable it in the last patch */
-#define has_transparent_hugepage() 0
+extern int has_transparent_hugepage(void);
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
 static inline pte_t pmd_pte(pmd_t pmd)
diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
index e4d3e9fb59be..074a4a225054 100644
--- a/arch/powerpc/mm/pgtable_64.c
+++ b/arch/powerpc/mm/pgtable_64.c
@@ -831,4 +831,33 @@ pmd_t pmdp_get_and_clear(struct mm_struct *mm,
         memset(pgtable, 0, PTE_FRAG_SIZE);
         return old_pmd;
 }
+
+int has_transparent_hugepage(void)
+{
+        if (!mmu_has_feature(MMU_FTR_16M_PAGE))
+                return 0;
+        /*
+         * We support THP only if PMD_SIZE is 16MB.
+         */
+        if (mmu_psize_defs[MMU_PAGE_16M].shift != PMD_SHIFT)
+                return 0;
+        /*
+         * We need to make sure that we support 16MB hugepage in a segement
+         * with base page size 64K or 4K. We only enable THP with a PAGE_SIZE
+         * of 64K.
+         */
+        /*
+         * If we have 64K HPTE, we will be using that by default
+         */
+        if (mmu_psize_defs[MMU_PAGE_64K].shift &&
+            (mmu_psize_defs[MMU_PAGE_64K].penc[MMU_PAGE_16M] == -1))
+                return 0;
+        /*
+         * Ok we only have 4K HPTE
+         */
+        if (mmu_psize_defs[MMU_PAGE_4K].penc[MMU_PAGE_16M] == -1)
+                return 0;
+
+        return 1;
+}
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */