Oracle Database Discussions

i'm installing 10gR2 on SLES 10 x86_64 bit on a machine with 64 bit xeon processors and i'm a bit confused
about the setting of kernel parameter kernel.shmmax. According to note 373681.1 and other similar notes
of requirements for installations on linux 64 bit it seems that this values can be setted at a maximum of
4gb and i can't understand why. For what i know Oracle tries to allocate SGA on one large shared memory
segment and the parameter kernel.shmmax for what i've understand limits the maximum size of shared memory
segments, with kernel.shmall. So if i set kernel.shmmax to 4 GB i'm not able to set SGA_MAX_SIZE to a value
higher than 4 gb and this is not what i want.
So, why on all notes i've found on the web it is written to set the parameter to a values max of 4 GB????

Regards,
Cristian Cudizio