mm: compaction: use helper compound_nr in isolate_migratepages_block

Use helper compound_nr to make use of compound_nr when CONFIG_64BIT and
simplify the code a bit.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Miaohe Lin <[email protected]>
Cc: Charan Teja Kalla <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Pintu Kumar <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/compaction.c

@@ -908,7 +908,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 				 /* Do not report -EBUSY down the chain */
 				if (ret == -EBUSY)
 					ret = 0;
-				low_pfn += (1UL << compound_order(page)) - 1;
+				low_pfn += compound_nr(page) - 1;
 				goto isolate_fail;
 			}