Module Compilation Modules

[Can Sar]

I am running Ubuntu, and installed the linux headers for 2.6.8.1-3-386. 
I've been compiling and running modules for a few days, but am now 
getting the following error message:

make: Entering directory `/usr/src/linux-headers-2.6.8.1-3-386'
CC [M] /home/csar/modules/sbd.o
Building modules, stage 2.
MODPOST
*** Warning: "__pagevec_release" [/home/csar/modules/sbd.ko] undefined!
*** Warning: "pagevec_lookup_tag" [/home/csar/modules/sbd.ko] undefined!
LD [M] /home/csar/modules/sbd.ko
make: Leaving directory `/usr/src/linux-headers-2.6.8.1-3-386'

I am obviously using the functions __pagevec_release and 
pagevec_lookup_tag for my module, because I need to do some weird stuff 
to the buffer cache (this is for a research project). I am, however, 
entirely clueless as to what is causing this. I declared both of them 
as extern, but that didn't help at all.
I hope someone can help me.

Thanks,
Can