gcf2 + extsearch: check for unlinked files on Linux
Check for unlinked mmap-ed files via /proc/$PID/maps every 60s
or so.
ExtSearch (extindex) is compatible-enough with Inbox objects to
be wired into the old per-inbox code, but the startup cost is
projected to be much higher down the line when there's >30K
inboxes, so we scan /proc/$PID/maps for deleted files before
unlinking. With old Inbox objects, it was (and is) simpler to
just kill processes w/o checking due to the low startup cost
(and non-portability of checking).
Reported-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Link: https://public-inbox.org/meta/20210921144754.gulkneuulzo27qbw@meerkat.local/