Re: The Kernel (fwd)

[George Bonser <grep@oriole.sbay.org>]

On 23 Jan 1998 jfm2@club-internet.fr wrote:

> In RH all the SCSI drivers are modular so I stripped the modules and
> looked the size of the stuff: more than 500K.  That means than if you
> compile them in, every IDE user will have 500k of fat.  And than every
> SCSI user will have 400K in excess due to drivers for the other SCSI
> controllers.  Having 500 K of unsawappabel RAM in excess of what is
> needed (a bit less because ramdisk and initrd has some overhead) is
> something than makes kernel compiling mandatory for people with 8
> megs.  I am going for delivering the best kernel possible to SEUL
> users, not the one saving me work or the one decided by others.

Yeah, it pares the size of the kernel but it puts it back into the ramdisk
so the total memory usage increases because, you you pointed out, of the
ramdisk filesystem overhead.  I have already determined that Debian is in
fact using initrd.  I will have a look tonight to see what they put in the
modules directory of that root image that gets loaded to the ramdisk as
soon as slowpoke gets done with a project. (slowpoke is my sandbox
machine)

> Try a dummy install and when it asks you what CDROM you have then lie
> and tell than you have a proprietary CDROM.  It will ask you for
> another floppy.  There are distributions who need only one floppy
> whatever your CDROM is, or whatever your network card (only PCMCIA
> drivers are on an additional floppy) if you are installing with NFS.

Right, I think the trouble is that they can not fit ALL the modules onto
the one floppy.  There are a ton of modules on the debian floppy ...
serial, parallel, net cards, tons.  Bruce is pretty good about trying to
get the install down to a single floppy (except for the base install) ...
heck, if you have a bootable CDROM, you do not need any floppies for
Debian.  If your CDROM is not bootable, you will need at least one and
possibly two floppies. If you have no CDROM, you will need six or possibly
five and install the rest over FTP

> By the way the same applies to Redhat and Caldera.  Both allow to use
> every networking feature (in fact every feature known) out of the box
> without recompiling (I notice you did have to recompile for
> IP_Masquerading so Debian lacks some exotic networking features out of
> the box).

Caldera does have a modules diskette like Debian does.

Also, the latest Debian kernel (2.0.32 in 2.0) DOES have IP-Masquerading
enabled ... or at least IP firewalling.  As a matter of fact, they now use
an ipfwadm command to set up some anti-ip spoofing filters on bootup
(packets to/from 127.0.0.1 should never travel on eth0 ... etc).

I think that you might want to have a good look at what is currently
shipping from Debian.  It looks like they are moving in the direction that
you want it to.

 
> The following sizes are the file sizes of the kernels shipped with
> some distributions.  THis is not the same than the memory footprint of
> the kernel but this gives an idea:
> 
> Caldera kernel 2.0.29:  404158
> RedHat5 kernel 2.0.31:  444595
> Debian  kernel 2.0.30:  623026
> 
> Conclusion: Redhat and Caldera users get smaller kernels than Debian
> users.  They also get more networking features.  So more intensive use
> of modules makes kernel recompiling less necessary in Caldera or RedHat.

Have you seen the size of the patches that Debian applies to the standard
kernel?

I will have a look tomarrow sometime and document exactly what comes with
the kernel.  There is a basic security issue that I worry about if you
want to install an initrd kernel ... actually, I am not sure that initrd
looks for file ownership, only file name.

> 
> > I hear no great clamor of complaints on Debian-user about systems that
> > will not boot it.
> > 
> 
> How many beginners are using Debian?  The Debian population is
> essentially formed by people knowing how to recompile.

Good point.  Debian tends to be where people go when they get tired of the
endless hours of Slackware admin or Red Hat's package limitations. Most
Debian users are refugees from other systems ONLY because of dselect.  The
only time I have had to recompile is for IP-Masquerading when I used it.


> But those features are not needed by most people, specially SEUL users
> so I intend to gave them a second kernel close to optimal based on the
> equipment detected (automatic detection) and stripped of features
> needed only on routers or disk servers.

Sounds good ... that is something that can be worked on.  Once a method
for making boot disks for Debian 2.0 is released you should start working
on it.  You can grab Debian's kernel source package and the debian patch
and start looking at it now. We have a lot of other work to do before we
start to modify the kernel but it IS something that is going to need
doing.

> They will be able to boot on either one and get a fast and small
> kernel as long as they don't need exotic networking features.  The
> people in charge of routers are competent enough to recompile a kernel
> for obtaining better performance.

I agree with that. Lets keep in mind though that a prime application for
Linux is as a dial-on-deman IP-Masquerading router for homes with more
than one computer and only one phone line.

> If you are blunt I will be.  The Debian kernel in Debian 1.3 is one of
> the worse 2.0 kernels I have seen for targetting an end user.


I fail to see why.  It is a modular initrd kernel. It might have some
things built in that other modularize for performace reasons ... sometimes
the time it takes for a module to get loaded causes bad things to happen.
There might have been a tradeoff in general system performace from having
something built into the kernel vs. having it as a module.

For example, when someone installs a new kernel image on debian, it erases
the module deps so that they are rebuilt on bootup. If you have a modular
disk driver and you erase the module deps, you can not load that module.
You might not be able to shut down cleanly. 

There might be very good reasons why things like this are done.  They are
likely tradeoffs that cause a little inconveniance in one place but offer
what was decided to be a greater benefit in another.


George Bonser 
If NT is the answer, you didn't understand the question. (NOTE: Stolen sig)
http://www.debian.org
Debian/GNU Linux ... the maintainable operating system.