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-rw-r--r--mm/mmap.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/mm/mmap.c b/mm/mmap.c
index 126d8b976bfd..20ff0c33274c 100644
--- 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);
}