gparted/ext4 – Shrink partition to encrypted filesystem previous size after failed “move right” (undo extend)

After unsuccessfully try to “move right” large encrypted partition on my HDD, GParted show me this :
gparted

If I click on Partition > Information I have this message :

176.57 GiB of unallocated space within the partition.

information gparted

After brainstorming with myself, I finally want to recreate a new partition sdb7 having size of 176.57 GiB (like before) and keep sdb6 at original size (before failed operation).

How I can easily SHRINK my partition to exact filesystem size ? I found lot of resources to expand filesystem to partition size but not for shrinking… Important note is i’m using encrypted partition with luks….

I hesitate between multiple choices :

  1. Gparted > Resize/Move but I don’t know how to be sure operation will be quick, and exact size to setup.
  2. Maybe resize2fs -M /dev/sdb6 but I’m not sure it’s the right option to use.

Here more information about my FS :

Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype extent 64bit flex_bg sparse_super large_file huge_file dir_nlink extra_isize metadata_csum
Filesystem flags:         signed_directory_hash 
Default mount options:    user_xattr acl
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              93634560
Block count:              374506240
Reserved block count:     18725312
Free blocks:              209754695
Free inodes:              88553316
First block:              0
Block size:               4096
Fragment size:            4096
Group descriptor size:    64
Reserved GDT blocks:      1024
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         8192
Inode blocks per group:   512
Flex block group size:    16

Last detail : My GNU/Linux configuration is still booting like before (hopefully) so it’s because I need to use sdb7 from my windows installation.