Re: Recommendation for activating a deferred module init in the kernel

[Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>]

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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?

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre
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