From: Andrea Arcangeli <aarcange@redhat.com>

These returns 0 at compile time when the config option is disabled, to allow
gcc to eliminate the transparent hugepage function calls at compile time
without additional #ifdefs (only the export of those functions have to be
visible to gcc but they won't be required at link time and huge_memory.o can be
not built at all).

_PAGE_BIT_UNUSED1 is never used for pmd, only on pte.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
---

diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -168,6 +168,19 @@ extern void cleanup_highmap(void);
 #define	kc_offset_to_vaddr(o) ((o) | ~__VIRTUAL_MASK)
 
 #define __HAVE_ARCH_PTE_SAME
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline int pmd_trans_splitting(pmd_t pmd)
+{
+	return pmd_val(pmd) & _PAGE_SPLITTING;
+}
+
+static inline int pmd_trans_huge(pmd_t pmd)
+{
+	return pmd_val(pmd) & _PAGE_PSE;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* _ASM_X86_PGTABLE_64_H */
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -22,6 +22,7 @@
 #define _PAGE_BIT_PAT_LARGE	12	/* On 2MB or 1GB pages */
 #define _PAGE_BIT_SPECIAL	_PAGE_BIT_UNUSED1
 #define _PAGE_BIT_CPA_TEST	_PAGE_BIT_UNUSED1
+#define _PAGE_BIT_SPLITTING	_PAGE_BIT_UNUSED1 /* only valid on a PSE pmd */
 #define _PAGE_BIT_NX           63       /* No execute: only valid after cpuid check */
 
 /* If _PAGE_BIT_PRESENT is clear, we use these: */
@@ -45,6 +46,7 @@
 #define _PAGE_PAT_LARGE (_AT(pteval_t, 1) << _PAGE_BIT_PAT_LARGE)
 #define _PAGE_SPECIAL	(_AT(pteval_t, 1) << _PAGE_BIT_SPECIAL)
 #define _PAGE_CPA_TEST	(_AT(pteval_t, 1) << _PAGE_BIT_CPA_TEST)
+#define _PAGE_SPLITTING	(_AT(pteval_t, 1) << ...
[ message continues ]

Usually it is insisted upon that this looks like

static inline int pmd_trans_huge(pmd) {
	return 0;
}

I understand it's to avoid any possibility of side-effets though to have type
checking and I am 99% certain the compiler still does the right thing. Still,
with no obvious side-effects here;


-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
--

[ message continues ]

It doesn't seem to fail build on x86-64 and x86, so it should build
for all other archs too. I'm keeping this incremental at the end just
in case.

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -471,10 +471,20 @@ extern void untrack_pfn_vma(struct vm_ar
 #endif
 
 #ifndef CONFIG_TRANSPARENT_HUGEPAGE
-#define pmd_trans_huge(pmd) 0
-#define pmd_trans_splitting(pmd) 0
+static inline int pmd_trans_huge(pmd_t pmd)
+{
+	return 0;
+}
+static inline int pmd_trans_splitting(pmd_t pmd)
+{
+	return 0;
+}
 #ifndef __HAVE_ARCH_PMD_WRITE
-#define pmd_write(pmd)	({ BUG(); 0; })
+static inline int pmd_write(pmd_t pmd)
+{
+	BUG();
+	return 0;
+}
 #endif /* __HAVE_ARCH_PMD_WRITE */
 #endif
 
--

[ message continues ]