f2fs: add reserved_segments sysfs node

For the fine tuning of GC behavior, add reserved_segments sysfs node.
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -791,3 +791,9 @@ Description:	Controls migration window granularity of garbage collection on larg
 		section. it can control the scanning window granularity for GC migration
 		in a unit of segment, while migration_granularity controls the number
 		of segments which can be migrated at the same turn.
+
+What:		/sys/fs/f2fs/<disk>/reserved_segments
+Date:		September 2024
+Contact:	"Daeho Jeong" <daehojeong@google.com>
+Description:	In order to fine tune GC behavior, we can control the number of
+		reserved segments.

fs/f2fs/sysfs.c

@@ -986,6 +986,7 @@ SM_INFO_GENERAL_RW_ATTR(min_fsync_blocks);
 SM_INFO_GENERAL_RW_ATTR(min_seq_blocks);
 SM_INFO_GENERAL_RW_ATTR(min_hot_blocks);
 SM_INFO_GENERAL_RW_ATTR(min_ssr_sections);
+SM_INFO_GENERAL_RW_ATTR(reserved_segments);
 
 /* DCC_INFO ATTR */
 DCC_INFO_RW_ATTR(max_small_discards, max_discards);
@@ -1158,6 +1159,7 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(min_seq_blocks),
 	ATTR_LIST(min_hot_blocks),
 	ATTR_LIST(min_ssr_sections),
+	ATTR_LIST(reserved_segments),
 	ATTR_LIST(max_victim_search),
 	ATTR_LIST(migration_granularity),
 	ATTR_LIST(migration_window_granularity),