Re: [PATCH 0/3] build system: section garbage collection for vmlinux

[Adrian Bunk <bunk@kernel.org>]

On Wed, Sep 05, 2007 at 12:24:04PM -0700, Daniel Walker wrote:
> On Wed, 2007-09-05 at 21:31 +0200, Adrian Bunk wrote:
> > On Wed, Sep 05, 2007 at 08:14:12PM +0100, Denys Vlasenko wrote:
> > > On Wednesday 05 September 2007 19:38, Daniel Walker wrote:
> > > > > > You version doesn't work with CONFIG_MODULES right?
> > > > > 
> > > > > It works with CONFIG_MODULES.
> > > > 
> > > > Really? Take a look at this version,
> > > > 
> > > > http://lkml.org/lkml/2006/6/4/169
> > > > 
> > > > Marcello had to implement a two pass build to add back symbol used in
> > > > modules which got removed from the main kernel.. You don't appear to do
> > > > that. Marcelo also claims better size reduction than you.
> > > 
> > > This will discard EXPORT_SYMBOLs potentially used by
> > > out-of-tree modules.
> > > 
> > > I also saw ~10% size reductions, but then at run-time test modules
> > > failed to load, they didn't find needed symbols.
> > > 
> > > OTOH if I know that I am not going to be using such modules,
> > > then this can be done. Will require another CONFIG_xxx, though.
> > 
> > One point to keep in mind is that the space penalty of CONFIG_MODULES=y 
> > is so big that CONFIG_MODULES=n is actually the most interesting case 
> > for small systems that really need small kernels.
> 
> Marcelo's version actual deals with the CONFIG_MODULES=y penalty , which
> is interesting to me .. It removes symbols added for CONFIG_MODULES
> which actually aren't used .. So CONFIG_MODULES=y is just as interesting
> as without (to me at least..).

There's still stuff like kernel/module.c or the additional space each 
used EXPORT_SYMBOL takes that make CONFIG_MODULES=n kernels smaller.

But it depends on the use case:
If you are aiming for the smallest possible runtime memory usage 
CONFIG_MODULES=n is the best choice, while for some applications
where the bzimage (or similar) size is for some reason limited but
the size of the modules doesn't matter the approach you mention might 
be the best.

> Daniel

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed