mm,thp: reduce ifdef'ery for THP in generic code

- pgtable-generic.c: Fold individual #ifdef for each helper into a top
  level #ifdef. Makes code more readable

- Converted the stub helpers for !THP to BUILD_BUG() vs. runtime BUG()

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: http://lkml.kernel.org/r/20151009133450.GA8597@node
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

include/asm-generic/pgtable.h

@@ -30,9 +30,19 @@ extern int ptep_set_access_flags(struct vm_area_struct *vma,
 #endif
 
 #ifndef __HAVE_ARCH_PMDP_SET_ACCESS_FLAGS
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 extern int pmdp_set_access_flags(struct vm_area_struct *vma,
 				 unsigned long address, pmd_t *pmdp,
 				 pmd_t entry, int dirty);
+#else
+static inline int pmdp_set_access_flags(struct vm_area_struct *vma,
+					unsigned long address, pmd_t *pmdp,
+					pmd_t entry, int dirty)
+{
+	BUILD_BUG();
+	return 0;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
 #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
@@ -64,12 +74,12 @@ static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 		set_pmd_at(vma->vm_mm, address, pmdp, pmd_mkold(pmd));
 	return r;
 }
-#else /* CONFIG_TRANSPARENT_HUGEPAGE */
+#else
 static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 					    unsigned long address,
 					    pmd_t *pmdp)
 {
-	BUG();
+	BUILD_BUG();
 	return 0;
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
@@ -81,8 +91,21 @@ int ptep_clear_flush_young(struct vm_area_struct *vma,
 #endif
 
 #ifndef __HAVE_ARCH_PMDP_CLEAR_YOUNG_FLUSH
-int pmdp_clear_flush_young(struct vm_area_struct *vma,
-			   unsigned long address, pmd_t *pmdp);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+extern int pmdp_clear_flush_young(struct vm_area_struct *vma,
+				  unsigned long address, pmd_t *pmdp);
+#else
+/*
+ * Despite relevant to THP only, this API is called from generic rmap code
+ * under PageTransHuge(), hence needs a dummy implementation for !THP
+ */
+static inline int pmdp_clear_flush_young(struct vm_area_struct *vma,
+					 unsigned long address, pmd_t *pmdp)
+{
+	BUILD_BUG();
+	return 0;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
 #ifndef __HAVE_ARCH_PTEP_GET_AND_CLEAR
@@ -175,11 +198,11 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
 	pmd_t old_pmd = *pmdp;
 	set_pmd_at(mm, address, pmdp, pmd_wrprotect(old_pmd));
 }
-#else /* CONFIG_TRANSPARENT_HUGEPAGE */
+#else
 static inline void pmdp_set_wrprotect(struct mm_struct *mm,
 				      unsigned long address, pmd_t *pmdp)
 {
-	BUG();
+	BUILD_BUG();
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
@@ -248,7 +271,7 @@ static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
 #else /* CONFIG_TRANSPARENT_HUGEPAGE */
 static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
 {
-	BUG();
+	BUILD_BUG();
 	return 0;
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */

mm/pgtable-generic.c

@@ -82,12 +82,13 @@ pte_t ptep_clear_flush(struct vm_area_struct *vma, unsigned long address,
 }
 #endif
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+
 #ifndef __HAVE_ARCH_PMDP_SET_ACCESS_FLAGS
 int pmdp_set_access_flags(struct vm_area_struct *vma,
 			  unsigned long address, pmd_t *pmdp,
 			  pmd_t entry, int dirty)
 {
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	int changed = !pmd_same(*pmdp, entry);
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 	if (changed) {
@@ -95,10 +96,6 @@ int pmdp_set_access_flags(struct vm_area_struct *vma,
 		flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
 	}
 	return changed;
-#else /* CONFIG_TRANSPARENT_HUGEPAGE */
-	BUG();
-	return 0;
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 }
 #endif
 
@@ -107,11 +104,7 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma,
 			   unsigned long address, pmd_t *pmdp)
 {
 	int young;
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
-#else
-	BUG();
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 	young = pmdp_test_and_clear_young(vma, address, pmdp);
 	if (young)
 		flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
@@ -120,7 +113,6 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma,
 #endif
 
 #ifndef __HAVE_ARCH_PMDP_HUGE_CLEAR_FLUSH
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
 			    pmd_t *pmdp)
 {
@@ -131,11 +123,9 @@ pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
 	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
 	return pmd;
 }
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
 #ifndef __HAVE_ARCH_PMDP_SPLITTING_FLUSH
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
 			  pmd_t *pmdp)
 {
@@ -145,11 +135,9 @@ void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
 	/* tlb flush only to serialize against gup-fast */
 	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
 }
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
 #ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
 				pgtable_t pgtable)
 {
@@ -162,11 +150,9 @@ void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
 		list_add(&pgtable->lru, &pmd_huge_pte(mm, pmdp)->lru);
 	pmd_huge_pte(mm, pmdp) = pgtable;
 }
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
 #ifndef __HAVE_ARCH_PGTABLE_WITHDRAW
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 /* no "address" argument so destroys page coloring of some arch */
 pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp)
 {
@@ -185,11 +171,9 @@ pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp)
 	}
 	return pgtable;
 }
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
 #ifndef __HAVE_ARCH_PMDP_INVALIDATE
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
 		     pmd_t *pmdp)
 {
@@ -197,11 +181,9 @@ void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
 	set_pmd_at(vma->vm_mm, address, pmdp, pmd_mknotpresent(entry));
 	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
 }
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
 #ifndef pmdp_collapse_flush
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
 			  pmd_t *pmdp)
 {
@@ -217,5 +199,5 @@ pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
 	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
 	return pmd;
 }
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */