> Plus, -s is the wrong way around.  That's an upper limit on the size
> of files you can store in tmpfs. The problem here is the reverse - not
> having enough free space reported in tmpfs because filecache (or some
> other better use of the memory) gobbled it all in the meantime.

can you explain how it's the reverse?
without trusting -s option, tmpfs have no way to know how much memory
it can grab.  note that allocating memory for tmpfs implies
reclaiming other use of memory including file cache.

YAMAMOTO Takashi