[arch-releng] reduce image size

[Christian Hesse]

Gerardo Exequiel Pozzi <vmlinuz386 at gmail.com> on Fri, 2015/10/02 16:22:
> On 10/02/2015 06:02 AM, Christian Hesse wrote:
> > Christian Hesse <list at eworm.de> on Thu, 2015/10/01 16:53:  
> >> Hello everybody,
> >>
> >> now that we support root filesystem on squashfs/overlayfs... Do we want
> >> to reduce image size some more?
> >>
> >> Currently we generate a squashfs for each architecture, one for x86_64
> >> and one for i686. How about merging these into one filesystem? Only
> >> extra thing to do is a bind mount for the subdirectory to /new_root.  
> > 
> > That's not true... We do not have to bind mount but add the arch to
> > path overlay mount options.
> >   
> >> The benefit is the deduplication support in squashfs, identical files are
> >> added to the filesystem just once. I did not yet test with the official
> >> media, but I'd expect the size to shrink about 120MB...  
> > 
> > I've build my own media and reduced size from 892M to 738M.
> >   
> >> This has a drawback, though: Copy-to-RAM would copy the files for both
> >> architectures, not just the needed one.  
> > 
> > To compare... To split airootfs.sfs image were about 400MB each... The
> > single one with both archs is 641MB.
> >   
> >> Any comments?  
> > 
> > Did some quick and dirty hacks:
> > 
> > https://github.com/eworm-de/archiso/commits/single-squashfs
> > 
> > This needs some polishing... Would be great to have a single switch to
> > decide whether or not the build a single airootfs.
> > 
> > Comments are still welcome. ;)
> >   
> 
> This is really great, the only downside is I am not sure how good for
> "releng" iso: for example for PXE setups,

I do use a modified nbd hook that allows to boot without copytoram... :-p

> more bw needed+more memory,
> more memory needed on copytoram,

That's what I was speaking about. No benefit without downside. :D

> and on loopback boot.

Really? IMHO you can boot in loopback mode without copytoram just fine.

> I agree in adding as optional feature, but not by default for "releng".

ACK. ;) Wondering whether or not I will use it by default for my own media...

So do you want me to polish this thing or do you want to implement a clean
solution yourself?
In first case I would like to discuss some details before.

Some general thoughts...
In make_prepare() we do a 'cp -a ...' - does that make sense? We can skip
that step when bootstrapping to the correct directory, no?
Moreover, sometimes we call 'mkarchiso -w "${work_dir}" ...' and add the
subdirectories later in function, sometimes we call 'mkarchiso -w
"${work_dir}/${arch}" ...' or similar. Is there a reason for that? To make
that path handling unique should simplify implementing my feature. This would
break existing configs, though.

> Thanks for your work!

No bit deal. I want to have the best live media myself. ;)
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