mm: move dummy_vm_ops out of a header

Otherwise the kernel ends up with multiple copies:
$ nm vmlinux | grep dummy_vm_ops
ffffffff81e4ea00 d dummy_vm_ops.2
ffffffff81e11760 d dummy_vm_ops.254
ffffffff81e406e0 d dummy_vm_ops.4
ffffffff81e3c780 d dummy_vm_ops.7

While here prefix it with vma_.

Link: https://lkml.kernel.org/r/20230806231611.1395735-1-mjguzik@gmail.comSigned-off-by: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -751,17 +751,17 @@ static inline struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 
 #endif /* CONFIG_PER_VMA_LOCK */
 
+extern const struct vm_operations_struct vma_dummy_vm_ops;
+
 /*
  * WARNING: vma_init does not initialize vma->vm_lock.
  * Use vm_area_alloc()/vm_area_free() if vma needs locking.
  */
 static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
 {
-	static const struct vm_operations_struct dummy_vm_ops = {};
-
 	memset(vma, 0, sizeof(*vma));
 	vma->vm_mm = mm;
-	vma->vm_ops = &dummy_vm_ops;
+	vma->vm_ops = &vma_dummy_vm_ops;
 	INIT_LIST_HEAD(&vma->anon_vma_chain);
 	vma_mark_detached(vma, false);
 	vma_numab_state_init(vma);

mm/init-mm.c

@@ -17,6 +17,8 @@
 #define INIT_MM_CONTEXT(name)
 #endif
 
+const struct vm_operations_struct vma_dummy_vm_ops;
+
 /*
  * For dynamically allocated mm_structs, there is a dynamically sized cpumask
  * at the end of the structure, the size of which depends on the maximum CPU