> >  does your "mkfs.ext2" use a block device, rather than a raw device?
> 
> It's not mine but it does.

ok, then i think i understand the problem.
we should throttle activities creating dirty buffers.
maybe by having a flag for getblk and friends to tell
"we are not going to dirty the buffer".

what your patch does is the opposite.  ie. throttling attempts of
cleaning buffers.  i believe it makes the situation worse.

YAMAMOTO Takashi