svn commit: r189230 - head/sys/net

[Luigi Rizzo]

On Sun, Mar 01, 2009 at 01:33:49PM +0000, Robert Watson wrote:
> On Sun, 1 Mar 2009, Luigi Rizzo wrote:
...
> >any chance to do similar things for other key kernel structures, such as 
> >mbufs and struct bio ?
> >
> >As an example, "struct bio" would benefit from at least one extra intptr_t 
> >field to be used for classification purposes (see some recent work we have 
> >been doing on disk scheduling). This is a rather trivial and unintrusive 
> >change.
> >
> >struct mbuf would benefit from a 'length' field, replacing the hardcoded 
> >MLEN/MHLEN. This field would allow us to do several things, e.g.:
> 
> Jeff has a large work-in-progress on mbufs, and so I don't want to go near 
> that until all that work has shaken out.  This includes support for 
> variable-size mbufs and eliminating large amounts of cluster use (while 
> retaining support for external storage, a we require that for zero-copy 
> foo). If you haven't seen his posts about that work, you might want to give 
> them a skim -- I think they were on arch@/net at .

ok thanks -- i did not see the posts but the things you explain are
perfectly in sync with what I had in mind.

> I thought bio was less sensitive to change since it was centrally allocated 
> these days, or is that not the case?

you are probably right, probably it's just the case to add the field
at the end so binary geom modules will not be affected by the change.

cheers
luigi