Running MySQL on a 32-Bit-Linux will probably impose a 2GB limit for
innodb_buffer_pool_size (seen on Debian + Ubuntu), even though you
already installed the bigmem kernel.
Assuming more RAM is available and you desperately want to use it, it’s worth downloading the Intel-compiled community server edition.
I was able to reserve 6GB for the InnoDB pool with that piece of software on a 32-Bit-Debian with bigmem kernel and the Intel-compiler is known to provide extra performance also in non-memory-related areas.