On Sun, Dec 02, 2007 at 06:34:40PM +0200, Jukka Marin wrote:
> If I could limit the softdep flush to always keep some 10% of disk I/O
> available, the machine would not stop completely during the flush operation.
> 
> while (something_to_be_flushed) {
>   if (systat_disk_%busy >= 90) {
>     sleep_before_next_flush(a_bit);
>   }
>   flush_some_data();
> };

except what you really need is more like:

while (something_to_be_flushed) {
  if (systat_disk_%busy >= 90) {
	temporarily_let_new_io_bypass_softdep()
  }
  else
    turn_off_bypass()
  flush_some_data();
};

eric