mm/compaction: remove unnecessary cursor page in isolate_freepages_block

The cursor is only used for page forward currently.  We can simply move
page forward directly to remove unnecessary cursor.

Link: https://lkml.kernel.org/r/20230803094901.2915942-4-shikemeng@huaweicloud.comSigned-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Kemeng Shi <shikemeng@huawei.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/compaction.c

@@ -589,7 +589,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 				bool strict)
 {
 	int nr_scanned = 0, total_isolated = 0;
-	struct page *cursor;
+	struct page *page;
 	unsigned long flags = 0;
 	bool locked = false;
 	unsigned long blockpfn = *start_pfn;
@@ -599,12 +599,11 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 	if (strict)
 		stride = 1;
 
-	cursor = pfn_to_page(blockpfn);
+	page = pfn_to_page(blockpfn);
 
 	/* Isolate free pages. */
-	for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) {
+	for (; blockpfn < end_pfn; blockpfn += stride, page += stride) {
 		int isolated;
-		struct page *page = cursor;
 
 		/*
 		 * Periodically drop the lock (if held) regardless of its
@@ -629,7 +628,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 
 			if (likely(order <= MAX_ORDER)) {
 				blockpfn += (1UL << order) - 1;
-				cursor += (1UL << order) - 1;
+				page += (1UL << order) - 1;
 				nr_scanned += (1UL << order) - 1;
 			}
 			goto isolate_fail;
@@ -666,7 +665,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 		}
 		/* Advance to the end of split page */
 		blockpfn += isolated - 1;
-		cursor += isolated - 1;
+		page += isolated - 1;
 		continue;
 
 isolate_fail: