Re: Linux/Pro -- clusters

Daniel Phillips
2001-12-04T17:16:05Z

On December 4, 2001 04:19 pm, Jeff Garzik wrote:
> Daniel Phillips wrote:
> >
> > On December 4, 2001 03:09 am, Donald Becker wrote:
> > > To bring this branch back on point: we should distinguish between
> > > design for an arbitrary and unpredictable goal (e.g. 128 way SMP)
> > > vs. putting some design into things that we are supposed to already
> > > understan
> > > [...]
> > > a VFS layer that doesn't require the kernel to know a priori all of
> > > the filesystem types that might be loaded
> >
> > Right, there's a consensus that the fs includes have to fixed and that it
> > should be in 2.5.lownum. The precise plan isn't fully evolved yet ;)
> >
> > See fsdevel for the thread, 3-4 months ago. IIRC, the favored idea (Linus's)
> > was to make the generic struct inode part of the fs-specific inode instead of
> > the other way around, which resolves the question of how the compiler
> > calculates the size/layout of an inode.
> >
> > This is going to be a pervasive change that someone has to do all in one
> > day, so it remains to be seen when/if that is actually going to happen.
> >
> > It's also going to break every out-of-tree filesystem.
>
> ug. what's wrong with a single additional alloc for generic_ip? [if a
> filesystem needs to do multiple allocs post-conversion, somebody's doing
> something wrong]

Single additional alloc -> twice as many allocs, two slabs, more cachelines
dirty. This was hashed out on fsdevel, though apparently not to everyone's
satisfaction.

> Using generic_ip in its current form has the advantage of being able to
> create a nicely-aligned kmem cache for your private inode data.

I don't see why that's hard with the combined struct.

--
Daniel