mm: ignore VM_SOFTDIRTY on VMA merging

[karo-tx-linux.git] / mm / mmap.c

diff --git a/mm/mmap.c b/mm/mmap.c
index 126d8b976bfd6a186c80b5cd3444765eda428e0e..20ff0c33274c27cbb23a78335f484765dc9f9e27 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -894,7 +894,15 @@ again:                     remove_next = 1 + (end > next->vm_end);
 static inline int is_mergeable_vma(struct vm_area_struct *vma,
                        struct file *file, unsigned long vm_flags)
 {
-       if (vma->vm_flags ^ vm_flags)
+       /*
+        * VM_SOFTDIRTY should not prevent from VMA merging, if we
+        * match the flags but dirty bit -- the caller should mark
+        * merged VMA as dirty. If dirty bit won't be excluded from
+        * comparison, we increase pressue on the memory system forcing
+        * the kernel to generate new VMAs when old one could be
+        * extended instead.
+        */
+       if ((vma->vm_flags ^ vm_flags) & ~VM_SOFTDIRTY)
                return 0;
        if (vma->vm_file != file)
                return 0;
@@ -1083,7 +1091,7 @@ static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *
        return a->vm_end == b->vm_start &&
                mpol_equal(vma_policy(a), vma_policy(b)) &&
                a->vm_file == b->vm_file &&
-               !((a->vm_flags ^ b->vm_flags) & ~(VM_READ|VM_WRITE|VM_EXEC)) &&
+               !((a->vm_flags ^ b->vm_flags) & ~(VM_READ|VM_WRITE|VM_EXEC|VM_SOFTDIRTY)) &&
                b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT);
 }