/spare/repo/libata-dev branch 'master'

1 files changed, 11 insertions, 0 deletions

diff --git a/mm/memory.c b/mm/memory.c
index e046b7e4b530..a596c1172248 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -498,6 +498,17 @@ int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
         unsigned long addr = vma->vm_start;
         unsigned long end = vma->vm_end;
 
+        /*
+         * Don't copy ptes where a page fault will fill them correctly.
+         * Fork becomes much lighter when there are big shared or private
+         * readonly mappings. The tradeoff is that copy_page_range is more
+         * efficient than faulting.
+         */
+        if (!(vma->vm_flags & (VM_HUGETLB|VM_NONLINEAR|VM_RESERVED))) {
+                if (!vma->anon_vma)
+                        return 0;
+        }
+
         if (is_vm_hugetlb_page(vma))
                 return copy_hugetlb_page_range(dst_mm, src_mm, vma);