inodes: df -i vs inode-nr

[Marco Shaw]

Is there anything online that contrasts what "df -i" reports and the
values provided by /proc/sys/fs/inode-nr?  Is there a connection?  I
have a decent grasp on VFS-related "inodes" on disk, but inod-nr
reports in-memory inodes, and I don't understand what that means.

For a particular system, for example, df -i reports 1% to 4% inode
utilization for different FSs, while /proc/sys/fs/inode-nr reports 70%
used*.

For example, what happens when the inode-nr reports 100% used on a system?

Marco

(*)inode_used_percent = 100*(inode_alloc - inode_free)/inode_alloc