mm/hugetlb: clean up ARCH_HAS_GIGANTIC_PAGE

This moves the #ifdef in C code to a Kconfig dependency.  Also we move
the gigantic_page_supported() function to be arch specific.

This allows architectures to conditionally enable runtime allocation of
gigantic huge page.  Architectures like ppc64 supports different
gigantic huge page size (16G and 1G) based on the translation mode
selected.  This provides an opportunity for ppc64 to enable runtime
allocation only w.r.t 1G hugepage.

No functional change in this patch.

Link: http://lkml.kernel.org/r/1494995292-4443-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm64/Kconfig

@@ -13,7 +13,7 @@ config ARM64
 	select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_GCOV_PROFILE_ALL
-	select ARCH_HAS_GIGANTIC_PAGE
+	select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_SET_MEMORY
 	select ARCH_HAS_SG_CHAIN

arch/arm64/include/asm/hugetlb.h

@@ -83,4 +83,8 @@ extern void huge_ptep_set_wrprotect(struct mm_struct *mm,
 extern void huge_ptep_clear_flush(struct vm_area_struct *vma,
 				  unsigned long addr, pte_t *ptep);
 
+#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
+static inline bool gigantic_page_supported(void) { return true; }
+#endif
+
 #endif /* __ASM_HUGETLB_H */

arch/s390/Kconfig

@@ -68,7 +68,7 @@ config S390
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_GCOV_PROFILE_ALL
-	select ARCH_HAS_GIGANTIC_PAGE
+	select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_SET_MEMORY
 	select ARCH_HAS_SG_CHAIN

arch/s390/include/asm/hugetlb.h

@@ -112,4 +112,7 @@ static inline pte_t huge_pte_modify(pte_t pte, pgprot_t newprot)
 	return pte_modify(pte, newprot);
 }
 
+#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
+static inline bool gigantic_page_supported(void) { return true; }
+#endif
 #endif /* _ASM_S390_HUGETLB_H */

arch/x86/Kconfig

@@ -22,7 +22,7 @@ config X86_64
 	def_bool y
 	depends on 64BIT
 	# Options that are inherently 64-bit kernel only:
-	select ARCH_HAS_GIGANTIC_PAGE
+	select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA
 	select ARCH_SUPPORTS_INT128
 	select ARCH_USE_CMPXCHG_LOCKREF
 	select HAVE_ARCH_SOFT_DIRTY

arch/x86/include/asm/hugetlb.h

@@ -85,4 +85,8 @@ static inline void arch_clear_hugepage_flags(struct page *page)
 {
 }
 
+#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
+static inline bool gigantic_page_supported(void) { return true; }
+#endif
+
 #endif /* _ASM_X86_HUGETLB_H */

mm/hugetlb.c

@@ -1040,9 +1040,7 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
 		((node = hstate_next_node_to_free(hs, mask)) || 1);	\
 		nr_nodes--)
 
-#if defined(CONFIG_ARCH_HAS_GIGANTIC_PAGE) && \
-	((defined(CONFIG_MEMORY_ISOLATION) && defined(CONFIG_COMPACTION)) || \
-	defined(CONFIG_CMA))
+#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
 static void destroy_compound_gigantic_page(struct page *page,
 					unsigned int order)
 {
@@ -1174,8 +1172,7 @@ static int alloc_fresh_gigantic_page(struct hstate *h,
 	return 0;
 }
 
-static inline bool gigantic_page_supported(void) { return true; }
-#else
+#else /* !CONFIG_ARCH_HAS_GIGANTIC_PAGE */
 static inline bool gigantic_page_supported(void) { return false; }
 static inline void free_gigantic_page(struct page *page, unsigned int order) { }
 static inline void destroy_compound_gigantic_page(struct page *page,