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

This is available only on NOMMU kernels.

This value adjusts the excess page trimming behaviour of power-of-2 aligned NOMMU mmap allocations.

A value of 0 disables trimming of allocations entirely, while a value of 1 trims excess pages aggressively. Any value >= 1 acts as the watermark where trimming of allocations is initiated.

The default value is 1.

See Documentation/nommu-mmap.txt for more information.