On Wed, Jun 18, 2008 at 10:59:50AM +0100, David Woodhouse wrote:
> On Wed, 2008-06-18 at 10:57 +0200, Geert Uytterhoeven wrote:
> > On Wed, 18 Jun 2008, Adrian Bunk wrote:
> > > On Wed, Jun 18, 2008 at 09:20:22AM +0100, David Woodhouse wrote:
> > > > On Wed, 2008-06-18 at 09:47 +0300, Gilad Ben-Yossef wrote:
> > > > > This may sound like a stupid question, but why are you compiling the
> > > > > modules statically?
> > > >
> > > > I wondered that.
> > > >
> > > > One potential reason to avoid modules is that they waste RAM -- you have
> > > > to allocate an integral number of pages for each one, which means an
> > > > average of 2KiB wasted for each module you load. Although that isn't
> > > > much, it's not zero either. It might be possible to optimise that by
> > > > 'packing' module allocations, if you're careful about it.
> > > >...
> > > > So the only real reason I can see to avoid modules in the _current_
> > > > kernel would be the wasted RAM, which should be something we can
> > > > address.
> > > >...
> > >
> > > You miss the size increase imposed by CONFIG_MODULES=y.
> > >
> > > E.g. setting CONFIG_MODULES=y in the arm collie_defconfig will
> > > increase the size of vmlinux by 14% (sic).
> > >
> > > I haven't investigated why it takes that much space, but stuff like
> > > kernel/module.o taking 23kB and each EXPORT_SYMBOL requiring a few
> > > bytes simply cannot be completely eliminated.
> >
> > Sounds like we need a tool that strips out the unneeded symbols, given a list
> > of modules?
>
> And do the --gc-sections step again after that... :)
But even after all optimizations CONFIG_MODULES=y will still cause a
significant additional cost [1] when thinking in the dimensions of
Tim's "the 30 or so Linux-tiny patches that I use get me about 110k of
reductions. For me, this is about 5% of my kernel size" statement in
another thread.
> dwmw2
cu
Adrian
[1] as I said, kernel/module.o alone takes 23kB
--
"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
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