+Using "assume unchanged" bit
+----------------------------
+
+Many operations in git depend on your filesystem to have an
+efficient `lstat(2)` implementation, so that `st_mtime`
+information for working tree files can be cheaply checked to see
+if the file contents have changed from the version recorded in
+the index file. Unfortunately, some filesystems have
+inefficient `lstat(2)`. If your filesystem is one of them, you
+can set "assume unchanged" bit to paths you have not changed to
+cause git not to do this check. Note that setting this bit on a
+path does not mean git will check the contents of the file to
+see if it has changed -- it makes git to omit any checking and
+assume it has *not* changed. When you make changes to working
+tree files, you have to explicitly tell git about it by dropping
+"assume unchanged" bit, either before or after you modify them.
+
+In order to set "assume unchanged" bit, use `--assume-unchanged`
+option. To unset, use `--no-assume-unchanged`.
+
+The command looks at `core.ignorestat` configuration variable. When
+this is true, paths updated with `git-update-index paths...` and
+paths updated with other git commands that update both index and
+working tree (e.g. `git-apply --index`, `git-checkout-index -u`,
+and `git-read-tree -u`) are automatically marked as "assume
+unchanged". Note that "assume unchanged" bit is *not* set if
+`git-update-index --refresh` finds the working tree file matches
+the index (use `git-update-index --really-refresh` if you want
+to mark them as "assume unchanged").
+
+