f2fs: remove two steps to flush dirty data pages

If there is no cold page, we don't need to do a loop to flush dirty
data pages.

On /dev/pmem0,

1. dd if=/dev/zero of=/mnt/test/testfile bs=1M count=2048 conv=fsync
 Before : 1.1 GB/s
 After  : 1.2 GB/s

2. dd if=/dev/zero of=/mnt/test/testfile bs=1M count=2048
 Before : 2.2 GB/s
 After  : 2.3 GB/s
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -1326,10 +1326,9 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 	int cycled;
 	int range_whole = 0;
 	int tag;
-	int step = 0;
 
 	pagevec_init(&pvec, 0);
-next:
+
 	if (wbc->range_cyclic) {
 		writeback_index = mapping->writeback_index; /* prev offset */
 		index = writeback_index;
@@ -1384,9 +1383,6 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 				goto continue_unlock;
 			}
 
-			if (step == is_cold_data(page))
-				goto continue_unlock;
-
 			if (PageWriteback(page)) {
 				if (wbc->sync_mode != WB_SYNC_NONE)
 					f2fs_wait_on_page_writeback(page,
@@ -1421,11 +1417,6 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
 		cond_resched();
 	}
 
-	if (step < 1) {
-		step++;
-		goto next;
-	}
-
 	if (!cycled && !done) {
 		cycled = 1;
 		index = 0;