f2fs: add a mount option for rb-tree extent cache

This patch adds a mount option 'extent_cache' in f2fs.

It is try to use a rb-tree based extent cache to cache more mapping information
with less memory if this option is set, otherwise we will use the original one
extent info cache.

Suggested-by: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -57,6 +57,7 @@ enum {
 	Opt_flush_merge,
 	Opt_nobarrier,
 	Opt_fastboot,
+	Opt_extent_cache,
 	Opt_err,
 };
 
@@ -78,6 +79,7 @@ static match_table_t f2fs_tokens = {
 	{Opt_flush_merge, "flush_merge"},
 	{Opt_nobarrier, "nobarrier"},
 	{Opt_fastboot, "fastboot"},
+	{Opt_extent_cache, "extent_cache"},
 	{Opt_err, NULL},
 };
 
@@ -367,6 +369,9 @@ static int parse_options(struct super_block *sb, char *options)
 		case Opt_fastboot:
 			set_opt(sbi, FASTBOOT);
 			break;
+		case Opt_extent_cache:
+			set_opt(sbi, EXTENT_CACHE);
+			break;
 		default:
 			f2fs_msg(sb, KERN_ERR,
 				"Unrecognized mount option \"%s\" or missing value",
@@ -599,6 +604,8 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 		seq_puts(seq, ",nobarrier");
 	if (test_opt(sbi, FASTBOOT))
 		seq_puts(seq, ",fastboot");
+	if (test_opt(sbi, EXTENT_CACHE))
+		seq_puts(seq, ",extent_cache");
 	seq_printf(seq, ",active_logs=%u", sbi->active_logs);
 
 	return 0;