cvs commit: src/sys/conf NOTES files options src/sys/kern vfs_bio.c src/sys/ufs/ffs ffs_rawread.c ffs_vnops.c

[Tor.Egge at cvsup.no.freebsd.org]

> I am neither impressed nor thrilled by this.
> 
> We already have pretty firm plans for converting struct bio from a
> "mapped KVM" to a a "virtual/physical scatter/gather" thing in the
> 6-current, and that is the correct way to solve this problem.

That doesn't help getting the data to the userland buffer instead of
into the buffer cache.

> If this is a crucial feature for 5-stable, I would far rather add
> we push ahead with that plan, than see more pbuf based hacks in the
> kernel.

Applications that perform their own caching can have a very low hit
rate in the buffer cache, and at some point the memory bandwith usage
copying data from the buffer cache to userland becomes much more
significant than the occational buffer cache hit.

- Tor Egge