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

[Adrian Bunk <bunk@kernel.org>]

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.

> dwmw2

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
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       "Only a promise," Lao Er said.
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