mm/hugetlb: reduce arch dependent code around follow_huge_*

Currently we have many duplicates in definitions around
follow_huge_addr(), follow_huge_pmd(), and follow_huge_pud(), so this
patch tries to remove the m.  The basic idea is to put the default
implementation for these functions in mm/hugetlb.c as weak symbols
(regardless of CONFIG_ARCH_WANT_GENERAL_HUGETL B), and to implement
arch-specific code only when the arch needs it.

For follow_huge_addr(), only powerpc and ia64 have their own
implementation, and in all other architectures this function just returns
ERR_PTR(-EINVAL).  So this patch sets returning ERR_PTR(-EINVAL) as
default.

As for follow_huge_(pmd|pud)(), if (pmd|pud)_huge() is implemented to
always return 0 in your architecture (like in ia64 or sparc,) it's never
called (the callsite is optimized away) no matter how implemented it is.
So in such architectures, we don't need arch-specific implementation.

In some architecture (like mips, s390 and tile,) their current
arch-specific follow_huge_(pmd|pud)() are effectively identical with the
common code, so this patch lets these architecture use the common code.

One exception is metag, where pmd_huge() could return non-zero but it
expects follow_huge_pmd() to always return NULL.  This means that we need
arch-specific implementation which returns NULL.  This behavior looks
strange to me (because non-zero pmd_huge() implies that the architecture
supports PMD-based hugepage, so follow_huge_pmd() can/should return some
relevant value,) but that's beyond this cleanup patch, so let's keep it.

Justification of non-trivial changes:
- in s390, follow_huge_pmd() checks !MACHINE_HAS_HPAGE at first, and this
  patch removes the check. This is OK because we can assume MACHINE_HAS_HPAGE
  is true when follow_huge_pmd() can be called (note that pmd_huge() has
  the same check and always returns 0 for !MACHINE_HAS_HPAGE.)
- in s390 and mips, we use HPAGE_MASK instead of PMD_MASK as done in common
  code. This patch forces these archs use PMD_MASK, but it's OK because
  they are identical in both archs.
  In s390, both of HPAGE_SHIFT and PMD_SHIFT are 20.
  In mips, HPAGE_SHIFT is defined as (PAGE_SHIFT + PAGE_SHIFT - 3) and
  PMD_SHIFT is define as (PAGE_SHIFT + PAGE_SHIFT + PTE_ORDER - 3), but
  PTE_ORDER is always 0, so these are identical.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Steve Capper <steve.capper@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm/mm/hugetlbpage.c

@@ -36,12 +36,6 @@
  * of type casting from pmd_t * to pte_t *.
  */
 
-struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address,
-			      int write)
-{
-	return ERR_PTR(-EINVAL);
-}
-
 int pud_huge(pud_t pud)
 {
 	return 0;

arch/arm64/mm/hugetlbpage.c

@@ -38,12 +38,6 @@ int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep)
 }
 #endif
 
-struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address,
-			      int write)
-{
-	return ERR_PTR(-EINVAL);
-}
-
 int pmd_huge(pmd_t pmd)
 {
 	return !(pmd_val(pmd) & PMD_TABLE_BIT);

arch/ia64/mm/hugetlbpage.c

@@ -114,12 +114,6 @@ int pud_huge(pud_t pud)
 	return 0;
 }
 
-struct page *
-follow_huge_pmd(struct mm_struct *mm, unsigned long address, pmd_t *pmd, int write)
-{
-	return NULL;
-}
-
 void hugetlb_free_pgd_range(struct mmu_gather *tlb,
 			unsigned long addr, unsigned long end,
 			unsigned long floor, unsigned long ceiling)

arch/metag/mm/hugetlbpage.c

@@ -94,12 +94,6 @@ int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep)
 	return 0;
 }
 
-struct page *follow_huge_addr(struct mm_struct *mm,
-			      unsigned long address, int write)
-{
-	return ERR_PTR(-EINVAL);
-}
-
 int pmd_huge(pmd_t pmd)
 {
 	return pmd_page_shift(pmd) > PAGE_SHIFT;

arch/mips/mm/hugetlbpage.c

@@ -68,12 +68,6 @@ int is_aligned_hugepage_range(unsigned long addr, unsigned long len)
 	return 0;
 }
 
-struct page *
-follow_huge_addr(struct mm_struct *mm, unsigned long address, int write)
-{
-	return ERR_PTR(-EINVAL);
-}
-
 int pmd_huge(pmd_t pmd)
 {
 	return (pmd_val(pmd) & _PAGE_HUGE) != 0;
@@ -83,15 +77,3 @@ int pud_huge(pud_t pud)
 {
 	return (pud_val(pud) & _PAGE_HUGE) != 0;
 }
-
-struct page *
-follow_huge_pmd(struct mm_struct *mm, unsigned long address,
-		pmd_t *pmd, int write)
-{
-	struct page *page;
-
-	page = pte_page(*(pte_t *)pmd);
-	if (page)
-		page += ((address & ~HPAGE_MASK) >> PAGE_SHIFT);
-	return page;
-}

arch/powerpc/mm/hugetlbpage.c

@@ -714,6 +714,14 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
 	return NULL;
 }
 
+struct page *
+follow_huge_pud(struct mm_struct *mm, unsigned long address,
+		pud_t *pud, int write)
+{
+	BUG();
+	return NULL;
+}
+
 static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
 				      unsigned long sz)
 {

arch/s390/mm/hugetlbpage.c

@@ -192,12 +192,6 @@ int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep)
 	return 0;
 }
 
-struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address,
-			      int write)
-{
-	return ERR_PTR(-EINVAL);
-}
-
 int pmd_huge(pmd_t pmd)
 {
 	if (!MACHINE_HAS_HPAGE)
@@ -210,17 +204,3 @@ int pud_huge(pud_t pud)
 {
 	return 0;
 }
-
-struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
-			     pmd_t *pmdp, int write)
-{
-	struct page *page;
-
-	if (!MACHINE_HAS_HPAGE)
-		return NULL;
-
-	page = pmd_page(*pmdp);
-	if (page)
-		page += ((address & ~HPAGE_MASK) >> PAGE_SHIFT);
-	return page;
-}

arch/sh/mm/hugetlbpage.c

@@ -67,12 +67,6 @@ int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep)
 	return 0;
 }
 
-struct page *follow_huge_addr(struct mm_struct *mm,
-			      unsigned long address, int write)
-{
-	return ERR_PTR(-EINVAL);
-}
-
 int pmd_huge(pmd_t pmd)
 {
 	return 0;
@@ -82,9 +76,3 @@ int pud_huge(pud_t pud)
 {
 	return 0;
 }
-
-struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
-			     pmd_t *pmd, int write)
-{
-	return NULL;
-}

arch/sparc/mm/hugetlbpage.c

@@ -215,12 +215,6 @@ pte_t huge_ptep_get_and_clear(struct mm_struct *mm, unsigned long addr,
 	return entry;
 }
 
-struct page *follow_huge_addr(struct mm_struct *mm,
-			      unsigned long address, int write)
-{
-	return ERR_PTR(-EINVAL);
-}
-
 int pmd_huge(pmd_t pmd)
 {
 	return 0;
@@ -230,9 +224,3 @@ int pud_huge(pud_t pud)
 {
 	return 0;
 }
-
-struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
-			     pmd_t *pmd, int write)
-{
-	return NULL;
-}

arch/tile/mm/hugetlbpage.c

@@ -150,12 +150,6 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
 	return NULL;
 }
 
-struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address,
-			      int write)
-{
-	return ERR_PTR(-EINVAL);
-}
-
 int pmd_huge(pmd_t pmd)
 {
 	return !!(pmd_val(pmd) & _PAGE_HUGE_PAGE);
@@ -166,28 +160,6 @@ int pud_huge(pud_t pud)
 	return !!(pud_val(pud) & _PAGE_HUGE_PAGE);
 }
 
-struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
-			     pmd_t *pmd, int write)
-{
-	struct page *page;
-
-	page = pte_page(*(pte_t *)pmd);
-	if (page)
-		page += ((address & ~PMD_MASK) >> PAGE_SHIFT);
-	return page;
-}
-
-struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address,
-			     pud_t *pud, int write)
-{
-	struct page *page;
-
-	page = pte_page(*(pte_t *)pud);
-	if (page)
-		page += ((address & ~PUD_MASK) >> PAGE_SHIFT);
-	return page;
-}
-
 int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep)
 {
 	return 0;

arch/x86/mm/hugetlbpage.c

@@ -52,20 +52,8 @@ int pud_huge(pud_t pud)
 	return 0;
 }
 
-struct page *
-follow_huge_pmd(struct mm_struct *mm, unsigned long address,
-		pmd_t *pmd, int write)
-{
-	return NULL;
-}
 #else
 
-struct page *
-follow_huge_addr(struct mm_struct *mm, unsigned long address, int write)
-{
-	return ERR_PTR(-EINVAL);
-}
-
 int pmd_huge(pmd_t pmd)
 {
 	return !!(pmd_val(pmd) & _PAGE_PSE);

mm/hugetlb.c

@@ -3660,7 +3660,20 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
 	return (pte_t *) pmd;
 }
 
-struct page *
+#endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
+
+/*
+ * These functions are overwritable if your architecture needs its own
+ * behavior.
+ */
+struct page * __weak
+follow_huge_addr(struct mm_struct *mm, unsigned long address,
+			      int write)
+{
+	return ERR_PTR(-EINVAL);
+}
+
+struct page * __weak
 follow_huge_pmd(struct mm_struct *mm, unsigned long address,
 		pmd_t *pmd, int write)
 {
@@ -3672,7 +3685,7 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
 	return page;
 }
 
-struct page *
+struct page * __weak
 follow_huge_pud(struct mm_struct *mm, unsigned long address,
 		pud_t *pud, int write)
 {
@@ -3684,19 +3697,6 @@ follow_huge_pud(struct mm_struct *mm, unsigned long address,
 	return page;
 }
 
-#else /* !CONFIG_ARCH_WANT_GENERAL_HUGETLB */
-
-/* Can be overriden by architectures */
-struct page * __weak
-follow_huge_pud(struct mm_struct *mm, unsigned long address,
-	       pud_t *pud, int write)
-{
-	BUG();
-	return NULL;
-}
-
-#endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
-
 #ifdef CONFIG_MEMORY_FAILURE
 
 /* Should be called in hugetlb_lock */