Defines part of a system threshold that immediately frees pages after an I/O completes instead of storing the pages for possible reuse. The threshold is lotsfree + pages_before_pager. The NFS environment also uses this threshold to curtail its asynchronous activities as memory pressure mounts.
1 to amount of physical memory
You might change this parameter when the majority of I/O is done for pages that are truly read or written once and never referenced again. Setting this variable to a larger amount of memory keeps adding pages to the free list.
You might also change this parameter when the system is subject to bursts of severe memory pressure. A larger value here helps maintain a larger cushion against the pressure.