[PATCH] Hugetlb: Reorganize hugetlb_fault to prepare for COW

This patch splits the "no_page()" type activity into its own function,
hugetlb_no_page().  hugetlb_fault() becomes the entry point for hugetlb faults
and delegates to the appropriate handler depending on the type of fault.
Right now we still have only hugetlb_no_page() but a later patch introduces a
COW fault.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Adam Litke <agl@us.ibm.com>
Cc: William Lee Irwin III <wli@holomorphy.com>
Cc: "Seth, Rohit" <rohit.seth@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 25 insertions, 9 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index fdbbbb90caa2..cf8225108b2f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -376,20 +376,15 @@ out:
         return page;
 }
 
-int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
-                        unsigned long address, int write_access)
+int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
+                        unsigned long address, pte_t *ptep)
 {
         int ret = VM_FAULT_SIGBUS;
         unsigned long idx;
         unsigned long size;
-        pte_t *pte;
         struct page *page;
         struct address_space *mapping;
 
-        pte = huge_pte_alloc(mm, address);
-        if (!pte)
-                goto out;
-
         mapping = vma->vm_file->f_mapping;
         idx = ((address - vma->vm_start) >> HPAGE_SHIFT)
                 + (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
@@ -408,11 +403,11 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                 goto backout;
 
         ret = VM_FAULT_MINOR;
-        if (!pte_none(*pte))
+        if (!pte_none(*ptep))
                 goto backout;
 
         add_mm_counter(mm, file_rss, HPAGE_SIZE / PAGE_SIZE);
-        set_huge_pte_at(mm, address, pte, make_huge_pte(vma, page));
+        set_huge_pte_at(mm, address, ptep, make_huge_pte(vma, page));
         spin_unlock(&mm->page_table_lock);
         unlock_page(page);
 out:
@@ -426,6 +421,27 @@ backout:
         goto out;
 }
 
+int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
+                        unsigned long address, int write_access)
+{
+        pte_t *ptep;
+        pte_t entry;
+
+        ptep = huge_pte_alloc(mm, address);
+        if (!ptep)
+                return VM_FAULT_OOM;
+
+        entry = *ptep;
+        if (pte_none(entry))
+                return hugetlb_no_page(mm, vma, address, ptep);
+
+        /*
+         * We could get here if another thread instantiated the pte
+         * before the test above.
+         */
+        return VM_FAULT_MINOR;
+}
+
 int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                         struct page **pages, struct vm_area_struct **vmas,
                         unsigned long *position, int *length, int i)