You cannot do this with the existing filesystem.

EXT at creation time defines a relationship between inodes and free space. This relationship tells the system where to find any particular inode as an offset from the start. Changing the relationship (so that you have fewer inodes) would invalidate existing inodes, so is not possible.

Unfortunately this means that the maximum number of inodes (2^32) may limit your filesystem before other limits are reached.

From an IBM support document with reference to this problem:

recreating new filesystem is only way to set new bytes-per-inode, make backup plan properly before recreating filesystem

You cannot do this with the existing filesystem.

EXT at creation time defines a relationship between inodes and free space. This relationship tells the system where to find any particular inode as an offset from the start. Changing the relationship (so that you have fewer inodes) would invalidate existing inodes, so is not possible.

Unfortunately this means that the maximum number of inodes (2³²) may limit your filesystem before other limits are reached.

From an IBM support document with reference to this problem:

recreating new filesystem is only way to set new bytes-per-inode, make backup plan properly before recreating filesystem