mm/hugetlb: take the free hpage during the iteration directly

Function dequeue_huge_page_node_exact() iterates the free list and return
the first valid free hpage.

Instead of break and check the loop variant, we could return in the loop
directly.  This could reduce some redundant check.

[mike.kravetz@oracle.com: points out a logic error]
[richard.weiyang@linux.alibaba.com: v4]
  Link: https://lkml.kernel.org/r/20200901014636.29737-8-richard.weiyang@linux.alibaba.comSigned-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Link: https://lkml.kernel.org/r/20200831022351.20916-8-richard.weiyang@linux.alibaba.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -1040,21 +1040,17 @@ static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
 		if (nocma && is_migrate_cma_page(page))
 			continue;
 
-		if (!PageHWPoison(page))
-			break;
-	}
+		if (PageHWPoison(page))
+			continue;
 
-	/*
-	 * if 'non-isolated free hugepage' not found on the list,
-	 * the allocation fails.
-	 */
-	if (&h->hugepage_freelists[nid] == &page->lru)
-		return NULL;
 		list_move(&page->lru, &h->hugepage_activelist);
 		set_page_refcounted(page);
 		h->free_huge_pages--;
 		h->free_huge_pages_node[nid]--;
 		return page;
+	}
+
+	return NULL;
 }
 
 static struct page *dequeue_huge_page_nodemask(struct hstate *h, gfp_t gfp_mask, int nid,