mm/mmap.c: make vma_merge() comment more easy to understand

Case 1/6, 2/7 and 3/8 have the same pattern and we handle them in the
same logic.

Rearrange the comment to make it a little easy for audience to
understand.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Wei Yang <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Darrick J. Wong <[email protected]>
Cc: Steve Capper <[email protected]>
Cc: Michel Lespinasse <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Yangtao Li <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/mmap.c

@@ -1091,15 +1091,18 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
  * the area passed down from mprotect_fixup, never extending beyond one
  * vma, PPPPPP is the prev vma specified, and NNNNNN the next vma after:
  *
- *     AAAA             AAAA                AAAA          AAAA
- *    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPPPNNNNNN    PPPPNNNNXXXX
- *    cannot merge    might become    might become    might become
- *                    PPNNNNNNNNNN    PPPPPPPPPPNN    PPPPPPPPPPPP 6 or
- *    mmap, brk or    case 4 below    case 5 below    PPPPPPPPXXXX 7 or
- *    mremap move:                                    PPPPXXXXXXXX 8
- *        AAAA
- *    PPPP    NNNN    PPPPPPPPPPPP    PPPPPPPPNNNN    PPPPNNNNNNNN
- *    might become    case 1 below    case 2 below    case 3 below
+ *     AAAA             AAAA                   AAAA
+ *    PPPPPPNNNNNN    PPPPPPNNNNNN       PPPPPPNNNNNN
+ *    cannot merge    might become       might become
+ *                    PPNNNNNNNNNN       PPPPPPPPPPNN
+ *    mmap, brk or    case 4 below       case 5 below
+ *    mremap move:
+ *                        AAAA               AAAA
+ *                    PPPP    NNNN       PPPPNNNNXXXX
+ *                    might become       might become
+ *                    PPPPPPPPPPPP 1 or  PPPPPPPPPPPP 6 or
+ *                    PPPPPPPPNNNN 2 or  PPPPPPPPXXXX 7 or
+ *                    PPPPNNNNNNNN 3     PPPPXXXXXXXX 8
  *
  * It is important for case 8 that the vma NNNN overlapping the
  * region AAAA is never going to extended over XXXX. Instead XXXX must