mm/mmap/vma_merge: fold curr, next assignment logic

Use find_vma_intersection() and vma_lookup() to both simplify the logic
and to fold the end == next->vm_start condition into one block.

This groups all of the simple range checks together and establishes the
invariant that, if prev, curr or next are non-NULL then their positions
are as expected.

This has no functional impact.

Link: https://lkml.kernel.org/r/c6d960641b4ba58fa6ad3d07bf68c27d847963c8.1679516210.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vernon Yang <vernon2gm@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index 030715027249fa24884ee5a6e41dca274f0d0ba3..e2e2c970374a07774552a4a3b826cfcc0910f4f9 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -917,15 +917,14 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
        if (vm_flags & VM_SPECIAL)
                return NULL;
 
-       curr = find_vma(mm, prev ? prev->vm_end : 0);
-       if (curr && curr->vm_end == end)                /* cases 6, 7, 8 */
-               next = find_vma(mm, curr->vm_end);
-       else
-               next = curr;
+       /* Does the input range span an existing VMA? (cases 5 - 8) */
+       curr = find_vma_intersection(mm, prev ? prev->vm_end : 0, end);
 
-       /* In cases 1 - 4 there's no CCCC vma */
-       if (curr && end <= curr->vm_start)
-               curr = NULL;
+       if (!curr ||                    /* cases 1 - 4 */
+           end == curr->vm_end)        /* cases 6 - 8, adjacent VMA */
+               next = vma_lookup(mm, end);
+       else
+               next = NULL;            /* case 5 */
 
        /* verify some invariant that must be enforced by the caller */
        VM_WARN_ON(prev && addr <= prev->vm_start);
@@ -946,11 +945,10 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
                }
        }
        /* Can we merge the successor? */
-       if (next && end == next->vm_start &&
-                       mpol_equal(policy, vma_policy(next)) &&
-                       can_vma_merge_before(next, vm_flags,
-                                            anon_vma, file, pgoff+pglen,
-                                            vm_userfaultfd_ctx, anon_name)) {
+       if (next && mpol_equal(policy, vma_policy(next)) &&
+           can_vma_merge_before(next, vm_flags,
+                                anon_vma, file, pgoff+pglen,
+                                vm_userfaultfd_ctx, anon_name)) {
                merge_next = true;
        }