file: /proc/sys/vm/overcommit_kbytes
variable: vm.overcommit_kbytes
Official reference

When overcommit_memory is set to 2, the committed address space is not permitted to exceed swap plus this amount of physical RAM. See below.

Note: overcommit_kbytes is the counterpart of overcommit_ratio. Only one of them may be specified at a time. Setting one disables the other (which then appears as 0 when read).