diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index ed70b68..4706d0a 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1313,8 +1313,11 @@ static void update_ckpt_flags(struct f2fs_sb_info *sbi, struct cp_control *cpc)
 	else
 		__clear_ckpt_flags(ckpt, CP_ORPHAN_PRESENT_FLAG);
 
-	if (is_sbi_flag_set(sbi, SBI_NEED_FSCK))
+	if (is_sbi_flag_set(sbi, SBI_NEED_FSCK) ||
+		is_sbi_flag_set(sbi, SBI_IS_RESIZEFS))
 		__set_ckpt_flags(ckpt, CP_FSCK_FLAG);
+	else
+		__clear_ckpt_flags(ckpt, CP_FSCK_FLAG);
 
 	if (is_sbi_flag_set(sbi, SBI_CP_DISABLED))
 		__set_ckpt_flags(ckpt, CP_DISABLED_FLAG);
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..387ec9a 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
@@ -1130,6 +1131,7 @@ enum {
 	SBI_QUOTA_NEED_FLUSH,			/* need to flush quota info in CP */
 	SBI_QUOTA_SKIP_FLUSH,			/* skip flushing quota in current CP */
 	SBI_QUOTA_NEED_REPAIR,			/* quota file may be corrupted */
+	SBI_IS_RESIZEFS,			/* resizefs is in process */
 };
 
 enum {
@@ -1309,6 +1311,7 @@ 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 */
+	struct mutex resize_mutex;		/* for resize exclusion */
 	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 +3178,8 @@ 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,
+					unsigned int start, unsigned int end);
 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..4a7ee7a 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -3013,6 +3013,26 @@ 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 (get_user(block_count, (__u64 __user *)arg))
+		return -EFAULT;
+
+	ret = f2fs_resize_fs(sbi, block_count);
+
+	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 +3089,8 @@ 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 +3204,7 @@ 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..c9282bc 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 = 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] %=
+				(MAIN_SECS(sbi) * sbi->segs_per_sec);
 			break;
 		}
 	}
@@ -1360,3 +1362,205 @@ 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;
+	int err = 0;
+
+	/* Move out cursegs from the target range */
+	for (type = CURSEG_HOT_DATA; type < NR_CURSEG_TYPE; type++)
+		allocate_segment_for_resize(sbi, type, start, end);
+
+	/* do GC to move out valid blocks in the range */
+	for (segno = start; segno <= end; segno += sbi->segs_per_sec) {
+		struct gc_inode_list gc_list = {
+			.ilist = LIST_HEAD_INIT(gc_list.ilist),
+			.iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
+		};
+
+		mutex_lock(&sbi->gc_mutex);
+		do_garbage_collect(sbi, segno, &gc_list, FG_GC);
+		mutex_unlock(&sbi->gc_mutex);
+		put_gc_inode(&gc_list);
+
+		if (get_valid_blocks(sbi, segno, true))
+			return -EAGAIN;
+	}
+
+	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;
+}
+
+static void update_raw_super_inc(struct f2fs_sb_info *sbi, unsigned int secs)
+{
+	struct f2fs_super_block *raw_sb = F2FS_RAW_SUPER(sbi);
+	u32 section_count = le32_to_cpu(raw_sb->section_count);
+	u32 segment_count = le32_to_cpu(raw_sb->segment_count);
+	u32 segment_count_main = le32_to_cpu(raw_sb->segment_count_main);
+	u64 block_count = le64_to_cpu(raw_sb->block_count);
+	unsigned int segs = secs * sbi->segs_per_sec;
+
+	raw_sb->section_count = cpu_to_le32(section_count + secs);
+	raw_sb->segment_count = cpu_to_le32(segment_count + segs);
+	raw_sb->segment_count_main = cpu_to_le32(segment_count_main + segs);
+	raw_sb->block_count = cpu_to_le64(block_count +
+						segs * sbi->blocks_per_seg);
+}
+
+static void update_raw_super_dec(struct f2fs_sb_info *sbi, unsigned int secs)
+{
+	struct f2fs_super_block *raw_sb = F2FS_RAW_SUPER(sbi);
+	u32 section_count = le32_to_cpu(raw_sb->section_count);
+	u32 segment_count = le32_to_cpu(raw_sb->segment_count);
+	u32 segment_count_main = le32_to_cpu(raw_sb->segment_count_main);
+	u64 block_count = le64_to_cpu(raw_sb->block_count);
+	unsigned int segs = secs * sbi->segs_per_sec;
+
+	raw_sb->section_count = cpu_to_le32(section_count - secs);
+	raw_sb->segment_count = cpu_to_le32(segment_count - segs);
+	raw_sb->segment_count_main = cpu_to_le32(segment_count_main - segs);
+	raw_sb->block_count = cpu_to_le64(block_count -
+						segs * sbi->blocks_per_seg);
+}
+
+static void update_fs_metadata_inc(struct f2fs_sb_info *sbi, unsigned int secs)
+{
+	unsigned int segs = secs * sbi->segs_per_sec;
+	u64 user_block_count = le64_to_cpu(F2FS_CKPT(sbi)->user_block_count);
+
+	SM_I(sbi)->segment_count += segs;
+	MAIN_SEGS(sbi) += segs;
+	FREE_I(sbi)->free_sections += secs;
+	FREE_I(sbi)->free_segments += segs;
+	F2FS_CKPT(sbi)->user_block_count = cpu_to_le64(user_block_count +
+						segs * sbi->blocks_per_seg);
+}
+
+static void update_fs_metadata_dec(struct f2fs_sb_info *sbi, unsigned int secs)
+{
+	unsigned int segs = secs * sbi->segs_per_sec;
+	u64 user_block_count = le64_to_cpu(F2FS_CKPT(sbi)->user_block_count);
+
+	SM_I(sbi)->segment_count -= segs;
+	MAIN_SEGS(sbi) -= segs;
+	FREE_I(sbi)->free_sections -= secs;
+	FREE_I(sbi)->free_segments -= segs;
+	F2FS_CKPT(sbi)->user_block_count = cpu_to_le64(user_block_count -
+						segs * sbi->blocks_per_seg);
+}
+
+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;
+
+	if (is_sbi_flag_set(sbi, SBI_NEED_FSCK)) {
+		f2fs_msg(sbi->sb, KERN_ERR,
+			"Should run fsck to repair first.");
+		return -EINVAL;
+	}
+
+	if (test_opt(sbi, DISABLE_CHECKPOINT)) {
+		f2fs_msg(sbi->sb, KERN_ERR,
+			"Checkpoint should be enabled.");
+		return -EINVAL;
+	}
+
+	freeze_bdev(sbi->sb->s_bdev);
+
+	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) {
+		thaw_bdev(sbi->sb->s_bdev, sbi->sb);
+		return err;
+	}
+
+	mutex_lock(&sbi->resize_mutex);
+	set_sbi_flag(sbi, SBI_IS_RESIZEFS);
+
+	mutex_lock(&DIRTY_I(sbi)->seglist_lock);
+
+	MAIN_SECS(sbi) -= secs;
+
+	for (gc_mode = 0; gc_mode < MAX_GC_POLICY; gc_mode++)
+		if (SIT_I(sbi)->last_victim[gc_mode] >=
+					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] >=
+					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, MAIN_SECS(sbi) * sbi->segs_per_sec,
+			MAIN_SEGS(sbi) - 1);
+	if (err)
+		goto out;
+
+	update_raw_super_dec(sbi, secs);
+	err = f2fs_commit_super(sbi, false);
+	if (err) {
+		update_raw_super_inc(sbi, secs);
+		goto out;
+	}
+
+	update_fs_metadata_dec(sbi, secs);
+
+	clear_sbi_flag(sbi, SBI_IS_RESIZEFS);
+	err = f2fs_sync_fs(sbi->sb, 1);
+	if (err) {
+		update_fs_metadata_inc(sbi, secs);
+		update_raw_super_inc(sbi, secs);
+		f2fs_commit_super(sbi, false);
+	}
+out:
+	if (err) {
+		set_sbi_flag(sbi, SBI_NEED_FSCK);
+		f2fs_msg(sbi->sb, KERN_ERR,
+				"resize_fs failed, should run fsck to repair!");
+
+		MAIN_SECS(sbi) += secs;
+		spin_lock(&sbi->stat_lock);
+		sbi->user_block_count += shrunk_blocks;
+		spin_unlock(&sbi->stat_lock);
+	}
+	clear_sbi_flag(sbi, SBI_IS_RESIZEFS);
+	mutex_unlock(&sbi->resize_mutex);
+	thaw_bdev(sbi->sb->s_bdev, sbi->sb);
+	return err;
+}
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 07e9235..00a3572 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -2651,6 +2651,40 @@ 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,
+					unsigned int start, unsigned int end)
+{
+	struct curseg_info *curseg = CURSEG_I(sbi, type);
+	unsigned int segno;
+
+	down_read(&SM_I(sbi)->curseg_lock);
+	mutex_lock(&curseg->curseg_mutex);
+	down_write(&SIT_I(sbi)->sentry_lock);
+
+	segno = CURSEG_I(sbi, type)->segno;
+	if (segno < start || segno > end)
+		goto unlock;
+
+	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);
+
+	locate_dirty_segment(sbi, segno);
+unlock:
+	up_write(&SIT_I(sbi)->sentry_lock);
+
+	if (segno != curseg->segno)
+		f2fs_msg(sbi->sb, KERN_NOTICE,
+			"For resize: curseg of type %d: %u ==> %u",
+			type, segno, curseg->segno);
+
+	mutex_unlock(&curseg->curseg_mutex);
+	up_read(&SM_I(sbi)->curseg_lock);
+}
+
 void f2fs_allocate_new_segments(struct f2fs_sb_info *sbi)
 {
 	struct curseg_info *curseg;
@@ -3774,7 +3808,7 @@ 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 = !is_sbi_flag_set(sbi, SBI_IS_RESIZEFS);
 	struct seg_entry *se;
 
 	down_write(&sit_i->sentry_lock);
@@ -3793,7 +3827,8 @@ 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) ||
+								!to_journal)
 		remove_sits_in_journal(sbi);
 
 	/*
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 1f581f0..5609774 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -3296,6 +3296,7 @@ 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);
 
@@ -3367,6 +3368,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 		set_sbi_flag(sbi, SBI_CP_DISABLED_QUICK);
 		sbi->interval_time[DISABLE_TIME] = DEF_DISABLE_QUICK_INTERVAL;
 	}
+	if (__is_set_ckpt_flags(F2FS_CKPT(sbi), CP_FSCK_FLAG))
+		set_sbi_flag(sbi, SBI_NEED_FSCK);
 
 	/* Initialize device list */
 	err = f2fs_scan_devices(sbi);
