vma_last_pgoff() already lives there, so it's a bit odd to keep
vma_start_pgoff() in mm/interval_tree.c. Move them together.

These each return unsigned long, which pgoff_t is typedef'd to. Make this
consistent and have these functions return pgoff_t instead.

Additionally, express vma_last_pgoff() in terms of vma_start_pgoff(), since
we wrap the vma->vm_pgoff access, we may as well use it here.

Also while we're here, const-ify the VMA and cleanup a bit.

No functional change intended.

Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
---
 include/linux/mm.h | 9 +++++++--
 mm/interval_tree.c | 5 -----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 485df9c2dbdd..059144435729 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4278,9 +4278,14 @@ static inline unsigned long vma_pages(const struct vm_area_struct *vma)
 	return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
 }
 
-static inline unsigned long vma_last_pgoff(struct vm_area_struct *vma)
+static inline pgoff_t vma_start_pgoff(const struct vm_area_struct *vma)
 {
-	return vma->vm_pgoff + vma_pages(vma) - 1;
+	return vma->vm_pgoff;
+}
+
+static inline pgoff_t vma_last_pgoff(const struct vm_area_struct *vma)
+{
+	return vma_start_pgoff(vma) + vma_pages(vma) - 1;
 }
 
 static inline unsigned long vma_desc_size(const struct vm_area_desc *desc)
diff --git a/mm/interval_tree.c b/mm/interval_tree.c
index 32bcfbfcf15f..344d1f5946c7 100644
--- a/mm/interval_tree.c
+++ b/mm/interval_tree.c
@@ -10,11 +10,6 @@
 #include <linux/rmap.h>
 #include <linux/interval_tree_generic.h>
 
-static inline unsigned long vma_start_pgoff(struct vm_area_struct *v)
-{
-	return v->vm_pgoff;
-}
-
 INTERVAL_TREE_DEFINE(struct vm_area_struct, shared.rb,
 		     unsigned long, shared.rb_subtree_last,
 		     vma_start_pgoff, vma_last_pgoff, /* empty */, vma_interval_tree)
-- 
2.54.0