CONFIG_SWAP is not available for thedefaultarchitecture x86.
Result is shown for architecture h8300

CONFIG_SWAP (not configurable)

modulename: page_io.ko

configname: CONFIG_SWAP

uClinux/h8300 (w/o MMU) Kernel Configuration
└─>SWAP
In linux kernel since version 2.6.12  
source code:
mm/
is selected by
CONFIG_MTD_SWAP