> It appears that if I mount /dev/wd0e on /mnt, and /dev is a tmpfs, changes
> in /mnt are not flushed to wd0a.  Instead, dirty blocks linger until I
> unmount /mnt.  I first noticed this because all of my tmpfs filesystems
> showed 0 blocks available as I extracted a large .tgz file under /mnt/.

if tmpfs ENOSPC is only symptom you see,
it's normal regarding buffer cache.

because tmpfs doesn't know the fact that some memory like buffer cache
can be reclaimed on-demand, it behaves too conservatively if memory is
filled up with caches.

YAMAMOTO Takashi