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.source