f2fs: clean up checkpoint flow

This patch cleans up checkpoint flow a bit:
- remove unneeded circulation of flushing meta pages.
- don't flush nat_bits pages in prior to other checkpoint pages.
- add bug_on to check remained meta pages after flushing.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -1329,11 +1329,9 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	int err;
 
 	/* Flush all the NAT/SIT pages */
-	while (get_pages(sbi, F2FS_DIRTY_META)) {
-		f2fs_sync_meta_pages(sbi, META, LONG_MAX, FS_CP_META_IO);
-		if (unlikely(f2fs_cp_error(sbi)))
-			break;
-	}
+	f2fs_sync_meta_pages(sbi, META, LONG_MAX, FS_CP_META_IO);
+	f2fs_bug_on(sbi, get_pages(sbi, F2FS_DIRTY_META) &&
+					!f2fs_cp_error(sbi));
 
 	/*
 	 * modify checkpoint
@@ -1406,14 +1404,6 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 		for (i = 0; i < nm_i->nat_bits_blocks; i++)
 			f2fs_update_meta_page(sbi, nm_i->nat_bits +
 					(i << F2FS_BLKSIZE_BITS), blk + i);
-
-		/* Flush all the NAT BITS pages */
-		while (get_pages(sbi, F2FS_DIRTY_META)) {
-			f2fs_sync_meta_pages(sbi, META, LONG_MAX,
-							FS_CP_META_IO);
-			if (unlikely(f2fs_cp_error(sbi)))
-				break;
-		}
 	}
 
 	/* write out checkpoint buffer at block 0 */
@@ -1449,6 +1439,8 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 
 	/* Here, we have one bio having CP pack except cp pack 2 page */
 	f2fs_sync_meta_pages(sbi, META, LONG_MAX, FS_CP_META_IO);
+	f2fs_bug_on(sbi, get_pages(sbi, F2FS_DIRTY_META) &&
+					!f2fs_cp_error(sbi));
 
 	/* wait for previous submitted meta pages writeback */
 	f2fs_wait_on_all_pages_writeback(sbi);