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

This is available only on NUMA kernels.

This is a percentage of the total pages in each zone. Zone reclaim will only occur if more than this percentage of pages are in a state that zone_reclaim_mode allows to be reclaimed.

If zone_reclaim_mode has the value 4 OR’d, then the percentage is compared against all file-backed unmapped pages including swapcache pages and tmpfs files. Otherwise, only unmapped pages backed by normal files but not tmpfs files and similar are considered.

The default is 1 percent.