diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
index 99e9a5c..7706049 100644
--- a/fs/f2fs/debug.c
+++ b/fs/f2fs/debug.c
@@ -27,8 +27,15 @@
 static void update_general_status(struct f2fs_sb_info *sbi)
 {
 	struct f2fs_stat_info *si = F2FS_STAT(sbi);
+	struct f2fs_super_block *raw_super = F2FS_RAW_SUPER(sbi);
 	int i;
 
+	/* these will be changed if online resize is done */
+	si->main_area_segs = le32_to_cpu(raw_super->segment_count_main);
+	si->main_area_sections = le32_to_cpu(raw_super->section_count);
+	si->main_area_zones = si->main_area_sections /
+				le32_to_cpu(raw_super->secs_per_zone);
+
 	/* validation check of the segment numbers */
 	si->hit_largest = atomic64_read(&sbi->read_hit_largest);
 	si->hit_cached = atomic64_read(&sbi->read_hit_cached);
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index a205d4d..fc53d37 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -423,6 +423,7 @@ static inline bool __has_cursum_space(struct f2fs_journal *journal,
 #define F2FS_IOC_SET_PIN_FILE		_IOW(F2FS_IOCTL_MAGIC, 13, __u32)
 #define F2FS_IOC_GET_PIN_FILE		_IOR(F2FS_IOCTL_MAGIC, 14, __u32)
 #define F2FS_IOC_PRECACHE_EXTENTS	_IO(F2FS_IOCTL_MAGIC, 15)
+#define F2FS_IOC_RESIZE_FS		_IOW(F2FS_IOCTL_MAGIC, 16, __u64)
 
 #define F2FS_IOC_SET_ENCRYPTION_POLICY	FS_IOC_SET_ENCRYPTION_POLICY
 #define F2FS_IOC_GET_ENCRYPTION_POLICY	FS_IOC_GET_ENCRYPTION_POLICY
@@ -1309,6 +1310,9 @@ struct f2fs_sb_info {
 	unsigned int segs_per_sec;		/* segments per section */
 	unsigned int secs_per_zone;		/* sections per zone */
 	unsigned int total_sections;		/* total section count */
+	unsigned int current_total_sections;	/* for shrink resize */
+	bool resizing;
+	struct mutex resize_mutex;
 	unsigned int total_node_count;		/* total node block count */
 	unsigned int total_valid_node_count;	/* valid node block count */
 	loff_t max_file_blocks;			/* max block index of file */
@@ -3175,6 +3179,7 @@ void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi,
 int f2fs_disable_cp_again(struct f2fs_sb_info *sbi, block_t unusable);
 void f2fs_release_discard_addrs(struct f2fs_sb_info *sbi);
 int f2fs_npages_for_summary_flush(struct f2fs_sb_info *sbi, bool for_ra);
+void allocate_segment_for_resize(struct f2fs_sb_info *sbi, int type);
 void f2fs_allocate_new_segments(struct f2fs_sb_info *sbi);
 int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range);
 bool f2fs_exist_trim_candidates(struct f2fs_sb_info *sbi,
@@ -3318,6 +3323,7 @@ int f2fs_migrate_page(struct address_space *mapping, struct page *newpage,
 int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, bool background,
 			unsigned int segno);
 void f2fs_build_gc_manager(struct f2fs_sb_info *sbi);
+int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count);
 
 /*
  * recovery.c
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index d05ac21..a37a0d4 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -3013,6 +3013,31 @@ static int f2fs_ioc_precache_extents(struct file *filp, unsigned long arg)
 	return f2fs_precache_extents(file_inode(filp));
 }
 
+static int f2fs_ioc_resize_fs(struct file *filp, unsigned long arg)
+{
+	struct f2fs_sb_info *sbi = F2FS_I_SB(file_inode(filp));
+	__u64 block_count;
+	int ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (f2fs_readonly(sbi->sb))
+		return -EROFS;
+
+	if (copy_from_user(&block_count, (__u64 __user *)arg, sizeof(__u64)))
+		return -EFAULT;
+
+	ret = mnt_want_write_file(filp);
+	if (ret)
+		return ret;
+
+	ret = f2fs_resize_fs(sbi, block_count);
+	mnt_drop_write_file(filp);
+
+	return ret;
+}
+
 long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	if (unlikely(f2fs_cp_error(F2FS_I_SB(file_inode(filp)))))
@@ -3069,6 +3094,8 @@ long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return f2fs_ioc_set_pin_file(filp, arg);
 	case F2FS_IOC_PRECACHE_EXTENTS:
 		return f2fs_ioc_precache_extents(filp, arg);
+	case F2FS_IOC_RESIZE_FS:
+		return f2fs_ioc_resize_fs(filp, arg);
 	default:
 		return -ENOTTY;
 	}
@@ -3182,6 +3209,7 @@ long f2fs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case F2FS_IOC_GET_PIN_FILE:
 	case F2FS_IOC_SET_PIN_FILE:
 	case F2FS_IOC_PRECACHE_EXTENTS:
+	case F2FS_IOC_RESIZE_FS:
 		break;
 	default:
 		return -ENOIOCTLCMD;
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 963fb45..273ca08 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -311,10 +311,11 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
 	struct sit_info *sm = SIT_I(sbi);
 	struct victim_sel_policy p;
 	unsigned int secno, last_victim;
-	unsigned int last_segment = MAIN_SEGS(sbi);
+	unsigned int last_segment;
 	unsigned int nsearched = 0;
 
 	mutex_lock(&dirty_i->seglist_lock);
+	last_segment = CUR_MAIN_SECS(sbi) * sbi->segs_per_sec;
 
 	p.alloc_mode = alloc_mode;
 	select_policy(sbi, gc_type, type, &p);
@@ -404,7 +405,8 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
 				sm->last_victim[p.gc_mode] = last_victim + 1;
 			else
 				sm->last_victim[p.gc_mode] = segno + 1;
-			sm->last_victim[p.gc_mode] %= MAIN_SEGS(sbi);
+			sm->last_victim[p.gc_mode] %=
+				(CUR_MAIN_SECS(sbi) * sbi->segs_per_sec);
 			break;
 		}
 	}
@@ -1360,3 +1362,134 @@ void f2fs_build_gc_manager(struct f2fs_sb_info *sbi)
 		SIT_I(sbi)->last_victim[ALLOC_NEXT] =
 				GET_SEGNO(sbi, FDEV(0).end_blk) + 1;
 }
+
+static int free_segment_range(struct f2fs_sb_info *sbi, unsigned int start,
+							unsigned int end)
+{
+	int type;
+	unsigned int segno, next_inuse;
+	struct gc_inode_list gc_list = {
+		.ilist = LIST_HEAD_INIT(gc_list.ilist),
+		.iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
+	};
+	int err = 0;
+
+	/* Move out cursegs from the target range */
+	for (type = CURSEG_HOT_DATA; type < NR_CURSEG_TYPE; type++) {
+		segno = CURSEG_I(sbi, type)->segno;
+		if (segno >= start && segno <= end)
+			allocate_segment_for_resize(sbi, type);
+	}
+
+	/* do GC to move out valid blocks in the range */
+	mutex_lock(&sbi->gc_mutex);
+	for (segno = start; segno <= end; segno += sbi->segs_per_sec) {
+		do_garbage_collect(sbi, segno, &gc_list, FG_GC);
+		if (get_valid_blocks(sbi, segno, true)) {
+			err = -EAGAIN;
+			break;
+		}
+	}
+
+	mutex_unlock(&sbi->gc_mutex);
+	put_gc_inode(&gc_list);
+
+	if (err)
+		return err;
+
+	err = f2fs_sync_fs(sbi->sb, 1);
+	if (err)
+		return err;
+
+	next_inuse = find_next_inuse(FREE_I(sbi), end + 1, start);
+	if (next_inuse <= end) {
+		f2fs_msg(sbi->sb, KERN_ERR,
+			"segno %u should be free but still inuse!", next_inuse);
+		f2fs_bug_on(sbi, 1);
+	}
+	return err;
+}
+
+int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
+{
+	__u64 old_block_count, shrunk_blocks;
+	unsigned int secs;
+	int gc_mode, gc_type;
+	int err = 0;
+
+	old_block_count = le64_to_cpu(F2FS_RAW_SUPER(sbi)->block_count);
+	if (block_count > old_block_count)
+		return -EINVAL;
+
+	/* new fs size should align to section size */
+	if (block_count % BLKS_PER_SEC(sbi))
+		return -EINVAL;
+
+	if (block_count == old_block_count)
+		return 0;
+
+	shrunk_blocks = old_block_count - block_count;
+	secs = shrunk_blocks / BLKS_PER_SEC(sbi);
+	spin_lock(&sbi->stat_lock);
+	if (shrunk_blocks + valid_user_blocks(sbi) +
+		sbi->current_reserved_blocks + sbi->unusable_block_count +
+		F2FS_OPTION(sbi).root_reserved_blocks > sbi->user_block_count)
+		err = -ENOSPC;
+	else
+		sbi->user_block_count -= shrunk_blocks;
+	spin_unlock(&sbi->stat_lock);
+	if (err)
+		return err;
+
+	mutex_lock(&sbi->resize_mutex);
+	sbi->resizing = true;
+	mutex_lock(&DIRTY_I(sbi)->seglist_lock);
+	CUR_MAIN_SECS(sbi) = MAIN_SECS(sbi) - secs;
+	for (gc_mode = 0; gc_mode < MAX_GC_POLICY; gc_mode++)
+		if (SIT_I(sbi)->last_victim[gc_mode] >=
+					CUR_MAIN_SECS(sbi) * sbi->segs_per_sec)
+			SIT_I(sbi)->last_victim[gc_mode] = 0;
+	for (gc_type = BG_GC; gc_type <= FG_GC; gc_type++)
+		if (sbi->next_victim_seg[gc_type] >=
+					CUR_MAIN_SECS(sbi) * sbi->segs_per_sec)
+			sbi->next_victim_seg[gc_type] = NULL_SEGNO;
+	mutex_unlock(&DIRTY_I(sbi)->seglist_lock);
+
+	err = free_segment_range(sbi, CUR_MAIN_SECS(sbi) * sbi->segs_per_sec,
+			MAIN_SEGS(sbi) - 1);
+	if (err) {
+		CUR_MAIN_SECS(sbi) = MAIN_SECS(sbi);
+		sbi->user_block_count += shrunk_blocks;
+		goto out;
+	}
+
+	/* Update superblock */
+	F2FS_RAW_SUPER(sbi)->section_count = cpu_to_le32(CUR_MAIN_SECS(sbi));
+	F2FS_RAW_SUPER(sbi)->segment_count = cpu_to_le32(le32_to_cpu(
+		F2FS_RAW_SUPER(sbi)->segment_count) - secs * sbi->segs_per_sec);
+	F2FS_RAW_SUPER(sbi)->segment_count_main = cpu_to_le32(
+					CUR_MAIN_SECS(sbi) * sbi->segs_per_sec);
+	F2FS_RAW_SUPER(sbi)->block_count =
+				cpu_to_le64(old_block_count - shrunk_blocks);
+	mutex_lock(&sbi->gc_mutex);
+	err = f2fs_commit_super(sbi, false);
+	mutex_unlock(&sbi->gc_mutex);
+	if (err) {
+		CUR_MAIN_SECS(sbi) = MAIN_SECS(sbi);
+		sbi->user_block_count += shrunk_blocks;
+		goto out;
+	}
+
+	/* Update FS metadata */
+	SM_I(sbi)->segment_count -= secs * sbi->segs_per_sec;
+	MAIN_SECS(sbi) = CUR_MAIN_SECS(sbi);
+	MAIN_SEGS(sbi) = MAIN_SECS(sbi) * sbi->segs_per_sec;
+	F2FS_CKPT(sbi)->user_block_count = cpu_to_le64(sbi->user_block_count);
+	FREE_I(sbi)->free_sections -= secs;
+	FREE_I(sbi)->free_segments -= secs * sbi->segs_per_sec;
+
+out:
+	sbi->resizing = false;
+	mutex_unlock(&sbi->resize_mutex);
+	return err;
+}
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 07e9235..2857465 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -2360,7 +2360,7 @@ static void get_new_segment(struct f2fs_sb_info *sbi,
 {
 	struct free_segmap_info *free_i = FREE_I(sbi);
 	unsigned int segno, secno, zoneno;
-	unsigned int total_zones = MAIN_SECS(sbi) / sbi->secs_per_zone;
+	unsigned int total_zones = CUR_MAIN_SECS(sbi) / sbi->secs_per_zone;
 	unsigned int hint = GET_SEC_FROM_SEG(sbi, *newseg);
 	unsigned int old_zoneno = GET_ZONE_FROM_SEG(sbi, *newseg);
 	unsigned int left_start = hint;
@@ -2377,12 +2377,13 @@ static void get_new_segment(struct f2fs_sb_info *sbi,
 			goto got_it;
 	}
 find_other_zone:
-	secno = find_next_zero_bit(free_i->free_secmap, MAIN_SECS(sbi), hint);
-	if (secno >= MAIN_SECS(sbi)) {
+	secno = find_next_zero_bit(free_i->free_secmap, CUR_MAIN_SECS(sbi),
+									hint);
+	if (secno >= CUR_MAIN_SECS(sbi)) {
 		if (dir == ALLOC_RIGHT) {
 			secno = find_next_zero_bit(free_i->free_secmap,
-							MAIN_SECS(sbi), 0);
-			f2fs_bug_on(sbi, secno >= MAIN_SECS(sbi));
+							CUR_MAIN_SECS(sbi), 0);
+			f2fs_bug_on(sbi, secno >= CUR_MAIN_SECS(sbi));
 		} else {
 			go_left = 1;
 			left_start = hint - 1;
@@ -2397,8 +2398,8 @@ static void get_new_segment(struct f2fs_sb_info *sbi,
 			continue;
 		}
 		left_start = find_next_zero_bit(free_i->free_secmap,
-							MAIN_SECS(sbi), 0);
-		f2fs_bug_on(sbi, left_start >= MAIN_SECS(sbi));
+							CUR_MAIN_SECS(sbi), 0);
+		f2fs_bug_on(sbi, left_start >= CUR_MAIN_SECS(sbi));
 		break;
 	}
 	secno = left_start;
@@ -2651,6 +2652,29 @@ static void allocate_segment_by_default(struct f2fs_sb_info *sbi,
 	stat_inc_seg_type(sbi, curseg);
 }
 
+void allocate_segment_for_resize(struct f2fs_sb_info *sbi, int type)
+{
+	struct curseg_info *curseg = CURSEG_I(sbi, type);
+	unsigned int old_segno = curseg->segno;
+
+	down_read(&SM_I(sbi)->curseg_lock);
+	mutex_lock(&curseg->curseg_mutex);
+	if (f2fs_need_SSR(sbi) && get_ssr_segment(sbi, type))
+		change_curseg(sbi, type);
+	else
+		new_curseg(sbi, type, true);
+
+	stat_inc_seg_type(sbi, curseg);
+	mutex_unlock(&curseg->curseg_mutex);
+	up_read(&SM_I(sbi)->curseg_lock);
+
+	if (get_valid_blocks(sbi, old_segno, false) == 0)
+		__set_test_and_free(sbi, old_segno);
+	f2fs_msg(sbi->sb, KERN_NOTICE,
+		"For resize: curseg of type %d: %u ==> %u",
+		type, old_segno, curseg->segno);
+}
+
 void f2fs_allocate_new_segments(struct f2fs_sb_info *sbi)
 {
 	struct curseg_info *curseg;
@@ -3774,7 +3798,7 @@ void f2fs_flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	struct f2fs_journal *journal = curseg->journal;
 	struct sit_entry_set *ses, *tmp;
 	struct list_head *head = &SM_I(sbi)->sit_entry_set;
-	bool to_journal = true;
+	bool to_journal = !sbi->resizing;
 	struct seg_entry *se;
 
 	down_write(&sit_i->sentry_lock);
@@ -3793,7 +3817,8 @@ void f2fs_flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	 * entries, remove all entries from journal and add and account
 	 * them in sit entry set.
 	 */
-	if (!__has_cursum_space(journal, sit_i->dirty_sentries, SIT_JOURNAL))
+	if (!__has_cursum_space(journal, sit_i->dirty_sentries, SIT_JOURNAL) ||
+								sbi->resizing)
 		remove_sits_in_journal(sbi);
 
 	/*
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 429007b..eaa9782 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -59,6 +59,7 @@
 
 #define MAIN_SEGS(sbi)	(SM_I(sbi)->main_segments)
 #define MAIN_SECS(sbi)	((sbi)->total_sections)
+#define CUR_MAIN_SECS(sbi)	((sbi)->current_total_sections)
 
 #define TOTAL_SEGS(sbi)							\
 	(SM_I(sbi) ? SM_I(sbi)->segment_count : 				\
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 1f581f0..c6201f0 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2843,6 +2843,8 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
 	sbi->segs_per_sec = le32_to_cpu(raw_super->segs_per_sec);
 	sbi->secs_per_zone = le32_to_cpu(raw_super->secs_per_zone);
 	sbi->total_sections = le32_to_cpu(raw_super->section_count);
+	sbi->current_total_sections = sbi->total_sections;
+	sbi->resizing = false;
 	sbi->total_node_count =
 		(le32_to_cpu(raw_super->segment_count_nat) / 2)
 			* sbi->blocks_per_seg * NAT_ENTRY_PER_BLOCK;
@@ -3296,6 +3298,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	mutex_init(&sbi->gc_mutex);
 	mutex_init(&sbi->writepages);
 	mutex_init(&sbi->cp_mutex);
+	mutex_init(&sbi->resize_mutex);
 	init_rwsem(&sbi->node_write);
 	init_rwsem(&sbi->node_change);
 
