> > - I see you have some XXX comments about tuning the amount of data to
> >   read ahead based on physical memory, which is true, but we should also
> >   tune based on the I/O throughput of the underlying device.  we want to
> >   be able to keep any device 100% busy, ideally without the user needing
> >   to configure this manually.  but we'll need some way to allow manual
> >   per-device tuning as well.
> 
> No, in point of fact, for NFS, I/O throughput rate is not enough: one
> really need to issue sufficient readahed to fill the bandwidth-delay product.

i don't think it needs a special treatment.
keeping devices busy and keeping network busy is the same thing
in the POV of read-ahead code.

YAMAMOTO Takashi