mm/swapfile: use vma iterator instead of vma linked list

unuse_mm() no longer needs to reference the linked list.

Link: https://lkml.kernel.org/r/20220906194824.2110408-64-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Tested-by: Yu Zhao <yuzhao@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/swapfile.c

@@ -1994,14 +1994,16 @@ static int unuse_mm(struct mm_struct *mm, unsigned int type)
 {
 	struct vm_area_struct *vma;
 	int ret = 0;
+	VMA_ITERATOR(vmi, mm, 0);
 
 	mmap_read_lock(mm);
-	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+	for_each_vma(vmi, vma) {
 		if (vma->anon_vma) {
 			ret = unuse_vma(vma, type);
 			if (ret)
 				break;
 		}
+
 		cond_resched();
 	}
 	mmap_read_unlock(mm);