Thanks for Bela and James's warm-hearted and constructional advice.
I'll lookup them up one by one.
About the disk's performance,ohh... The server is a HP DL380 G4, Raid
1, BDFLUSHR=30 and NAUTOUP=10, according to my inspection, the 100%
busy doesn't seem to be caused by the bdflush.. But I'm not sure. May
be really a hardware bottleneck ...

No matter what, I'll take your advice to heart and try to do
something, then I'll feedback the results to you, but this may take
some days because of the production environment.

Thanks to Bela,James and Bill again. Best regards for you.