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From: Daniel Phillips <phillips@bonn-fries.net>
To: Jeff Garzik <jgarzik@mandrakesoft.com>
Subject: Re: Linux/Pro  -- clusters
Date: Tue, 4 Dec 2001 18:16:32 +0100
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Cc: Donald Becker <becker@scyld.com>, Davide Libenzi <davidel@xmailserver.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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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
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