mm: make vma_merge() and split_vma() internal

Now the common pattern of - attempting a merge via vma_merge() and should
this fail splitting VMAs via split_vma() - has been abstracted, the former
can be placed into mm/internal.h and the latter made static.

In addition, the split_vma() nommu variant also need not be exported.

Link: https://lkml.kernel.org/r/405f2be10e20c4e9fbcc9fe6b2dfea105f6642e0.1697043508.git.lstoakes@gmail.comSigned-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -3235,16 +3235,7 @@ extern int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		      struct vm_area_struct *next);
 extern int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		       unsigned long start, unsigned long end, pgoff_t pgoff);
-extern struct vm_area_struct *vma_merge(struct vma_iterator *vmi,
-	struct mm_struct *, struct vm_area_struct *prev, unsigned long addr,
-	unsigned long end, unsigned long vm_flags, struct anon_vma *,
-	struct file *, pgoff_t, struct mempolicy *, struct vm_userfaultfd_ctx,
-	struct anon_vma_name *);
 extern struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *);
-extern int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *,
-		       unsigned long addr, int new_below);
-extern int split_vma(struct vma_iterator *vmi, struct vm_area_struct *,
-			 unsigned long addr, int new_below);
 extern int insert_vm_struct(struct mm_struct *, struct vm_area_struct *);
 extern void unlink_file_vma(struct vm_area_struct *);
 extern struct vm_area_struct *copy_vma(struct vm_area_struct **,

mm/internal.h

@@ -1002,6 +1002,15 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 				   unsigned long addr, pmd_t *pmd,
 				   unsigned int flags);
 
+/*
+ * mm/mmap.c
+ */
+struct vm_area_struct *vma_merge(struct vma_iterator *vmi,
+	struct mm_struct *, struct vm_area_struct *prev, unsigned long addr,
+	unsigned long end, unsigned long vm_flags, struct anon_vma *,
+	struct file *, pgoff_t, struct mempolicy *, struct vm_userfaultfd_ctx,
+	struct anon_vma_name *);
+
 enum {
 	/* mark page accessed */
 	FOLL_TOUCH = 1 << 16,

mm/mmap.c

@@ -2346,7 +2346,7 @@ static void unmap_region(struct mm_struct *mm, struct ma_state *mas,
  * has already been checked or doesn't make sense to fail.
  * VMA Iterator will point to the end VMA.
  */
-int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
+static int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		       unsigned long addr, int new_below)
 {
 	struct vma_prepare vp;
@@ -2428,7 +2428,7 @@ int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
  * Split a vma into two pieces at address 'addr', a new vma is allocated
  * either for the first part or the tail.
  */
-int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
+static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		     unsigned long addr, int new_below)
 {
 	if (vma->vm_mm->map_count >= sysctl_max_map_count)

mm/nommu.c

@@ -1305,7 +1305,7 @@ SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
  * split a vma into two pieces at address 'addr', a new vma is allocated either
  * for the first part or the tail.
  */
-int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
+static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		     unsigned long addr, int new_below)
 {
 	struct vm_area_struct *new;