> talking about mtime, i think it can be noted when the changes are
> flushed out to backing store.  ie. when we usually notice the dirtiness
> of the pages.

a problem is that there is no easy way to distinguish dirtied-via-write and
dirtied-via-mmap.
although a this-file-might-be-dirtied-via-mmap flag works for
most common usages, i guess.

YAMAMOTO Takashi