[RFC PATCH -V2 21/21] powerpc/THP: Enable THP on PPC64

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

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

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/pgtable.h |   33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index 5b8e93b..ae9114b 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h
@@ -107,8 +107,37 @@ static inline int pmd_trans_huge(pmd_t pmd)
 	return ((pmd_val(pmd) & PMD_ISHUGE) ==  PMD_ISHUGE);
 }
 
-/* We will enable it in the last patch */
-#define has_transparent_hugepage() 0
+static inline int has_transparent_hugepage(void)
+{
+	if (!mmu_has_feature(MMU_FTR_16M_PAGE))
+		return 0;
+	/*
+	 * We support THP only if HPAGE_SHIFT is 16MB.
+	 */
+	if (!HPAGE_SHIFT || (HPAGE_SHIFT != mmu_psize_defs[MMU_PAGE_16M].shift))
+		return 0;
+	/*
+	 * We need to make sure that we support 16MB huge page in a segement
+	 * with base page size 64K or 4K. We only enable THP with a PAGE_SIZE
+	 * of 64K.
+	 */
+	/* FIXME!! is the nonzero check always correct ? Can there be an machine
+	 * where penc is 0 ?
+	 */
+	/*
+	 * 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])
+		return 0;
+	/*
+	 * Ok we only have 4K HPTE
+	 */
+	if (!mmu_psize_defs[MMU_PAGE_4K].penc[MMU_PAGE_16M])
+		return 0;
+
+	return 1;
+}
 
 static inline pmd_t pmd_mkold(pmd_t pmd)
 {
-- 
1.7.10

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