> >> Below is an untested, almost certinaly broken, patch showing how
> >> FreeBSD 4.x does NFS readahead. It' basically two chunks:
> >
> >yes, i agree it's broken. :-)
> >we're not using traditional buffer cache interfaces for VREG's pages.
> 
> So how can we make it non-broken?

do readahead at upper layer (as we're doing now, or even more upper layer.)
maybe put some contexts into files/map entries, and use them to
determine how many pages to fetch?

> Or is adding more readahead
> here just not going to help an app doing dd= ... ?

i think it's worth to try to tweak genfs_rapages/genfs_racount.

YAMAMOTO Takashi