[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>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index fdbbbb9..cf82251 100644 (file)
--- 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)