This kernel contains changes to the kernel:

# Change the size of the kernel virtual address space.  Due to
# constraints in loader(8) on i386, this must be a multiple of 4.
# 256 = 1 GB of kernel address space.  Increasing this also causes
# a reduction of the address space in user processes.  512 splits
# the 4GB cpu address space in half (2GB user, 2GB kernel).

# Increae *4 default value, 4GB of ram
options         KVA_PAGES=1040
options         VM_KMEM_SIZE
options         VM_KMEM_SIZE_MAX
options         VM_KMEM_SIZE_SCALE

You may or may not need to increase:

  vm.kmem_size=123456789
  vm.kmem_size_max=1234567890

in
  /boot/loader.conf

To install, run these commands:

# Backup old kernel
mv /boot/kernel/kernel.gz /boot/kernel/kernel_old.tgz
# Fetch new kernel
fetch -ovv /boot/kernel/ \
http://www.pfsense.com/~sullrich/1.0_kernels/4096_users/kernel.gz