ido-max-dir-file-cache

ido-max-dir-file-cache is a variable defined in `ido.el'.
Its value is

100

Documentation:
Maximum number of working directories to be cached.

Uses keymap `ido-file-completion-map', which is not currently defined.

This is the size of the cache of `file-name-all-completions' results.
Each cache entry is time stamped with the modification time of the
directory. Some systems, like Windows, have unreliable directory
modification times, so you may choose to disable caching on such
systems, or explicitly refresh the cache contents using the command
`ido-reread-directory' command (M-x ido-reread-directory) in the minibuffer.
See also `ido-dir-file-cache' and `ido-save-directory-list-file'.

You can customize this variable.