Subject: [PATCH V4 3/3] powerpc/mm/hash: Don't memset pgd table if not needed

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 7 Mar 2018 17:44:40 +0530

We need to zero-out pgd table only if we share the slab cache with pud/pmd
level caches. With the support of 4PB, we don't share the slab cache anymore.
Instead of removing the code completely hide it within an #ifdef. We don't need
to do this with any other page table level, because they all allocate table
of double the size and we take of initializing the first half corrrectly during
page table zap.

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 arch/powerpc/include/asm/book3s/64/pgalloc.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/book3s/64/pgalloc.h b/arch/powerpc/include/asm/book3s/64/pgalloc.h
index 4746bc68d446..07f0dbac479f 100644
--- a/arch/powerpc/include/asm/book3s/64/pgalloc.h
+++ b/arch/powerpc/include/asm/book3s/64/pgalloc.h
@@ -80,8 +80,19 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 
 	pgd = kmem_cache_alloc(PGT_CACHE(PGD_INDEX_SIZE),
 			       pgtable_gfp_flags(mm, GFP_KERNEL));
+	/*
+	 * With hugetlb, we don't clear the second half of the page table.
+	 * If we share the same slab cache with the pmd or pud level table,
+	 * we need to make sure we zero out the full table on alloc.
+	 * With 4K we don't store slot in the second half. Hence we don't
+	 * need to do this for 4k.
+	 */
+#if (H_PGD_INDEX_SIZE == H_PUD_CACHE_INDEX) || \
+		(H_PGD_INDEX_SIZE == H_PMD_CACHE_INDEX)
+#if defined(CONFIG_HUGETLB_PAGE) && defined(CONFIG_PPC_64K_PAGES)
 	memset(pgd, 0, PGD_TABLE_SIZE);
-
+#endif
+#endif
 	return pgd;
 }
 
-- 
2.14.3