mm/mmap: leave adjust_next as virtual address instead of page frame number

Instead of converting adjust_next between bytes and pages number, let's
just store the virtual address into adjust_next.

Also, this patch fixes one typo in the comment of vma_adjust_trans_huge().

[vbabka@suse.cz: changelog tweak]

Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Link: http://lkml.kernel.org/r/20200828081031.11306-1-richard.weiyang@linux.alibaba.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -758,7 +758,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
 			 * vma expands, overlapping part of the next:
 			 * mprotect case 5 shifting the boundary up.
 			 */
-			adjust_next = (end - next->vm_start) >> PAGE_SHIFT;
+			adjust_next = (end - next->vm_start);
 			exporter = next;
 			importer = vma;
 			VM_WARN_ON(expand != importer);
@@ -768,7 +768,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
 			 * split_vma inserting another: so it must be
 			 * mprotect case 4 shifting the boundary down.
 			 */
-			adjust_next = -((vma->vm_end - end) >> PAGE_SHIFT);
+			adjust_next = -(vma->vm_end - end);
 			exporter = vma;
 			importer = next;
 			VM_WARN_ON(expand != importer);
@@ -840,8 +840,8 @@ again:
 	}
 	vma->vm_pgoff = pgoff;
 	if (adjust_next) {
-		next->vm_start += adjust_next << PAGE_SHIFT;
-		next->vm_pgoff += adjust_next;
+		next->vm_start += adjust_next;
+		next->vm_pgoff += adjust_next >> PAGE_SHIFT;
 	}
 
 	if (root) {