mm/mempolicy: clean up the code logic in queue_pages_pte_range

Since commit e5947d23 ("mm: mempolicy: don't have to split pmd for
huge zero page"), THP is never splited in queue_pages_pmd.  Thus 2 is
never returned now.  We can remove such unnecessary ret != 2 check and
clean up the relevant comment.  Minor improvements in readability.

Link: https://lkml.kernel.org/r/20220419122234.45083-1-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mempolicy.c

@@ -440,12 +440,11 @@ static inline bool queue_pages_required(struct page *page,
 }
 
 /*
- * queue_pages_pmd() has four possible return values:
+ * queue_pages_pmd() has three possible return values:
  * 0 - pages are placed on the right node or queued successfully, or
  *     special page is met, i.e. huge zero page.
  * 1 - there is unmovable page, and MPOL_MF_MOVE* & MPOL_MF_STRICT were
  *     specified.
- * 2 - THP was split.
  * -EIO - is migration entry or only MPOL_MF_STRICT was specified and an
  *        existing page was already on a node that does not follow the
  *        policy.
@@ -507,18 +506,13 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
 	struct page *page;
 	struct queue_pages *qp = walk->private;
 	unsigned long flags = qp->flags;
-	int ret;
 	bool has_unmovable = false;
 	pte_t *pte, *mapped_pte;
 	spinlock_t *ptl;
 
 	ptl = pmd_trans_huge_lock(pmd, vma);
-	if (ptl) {
-		ret = queue_pages_pmd(pmd, ptl, addr, end, walk);
-		if (ret != 2)
-			return ret;
-	}
-	/* THP was split, fall through to pte walk */
+	if (ptl)
+		return queue_pages_pmd(pmd, ptl, addr, end, walk);
 
 	if (pmd_trans_unstable(pmd))
 		return 0;