blaze authored Jan 31, 2018 and Ben Gamari committed Jan 31, 2018

Currently runtime keeps hold to 4*used_memory. This includes, in
particular, nursery, which can be quite large on multiprocessor
machines: 16 CPUs x 64Mb each is 1GB. Multiplying it by 4 means whatever
actual memory usage is, runtime will never release memory under 4GB, and
this is quite excessive for processes which only need a lot of memory
shortly (think building data structures from large files).

This diff makes multiplier to apply only to GC-managed memory, leaving
all "static" allocations alone.

Test Plan: make test TEST="T14702"

Reviewers: bgamari, erikd, simonmar

Reviewed By: simonmar

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: #14702

Differential Revision: https://phabricator.haskell.org/D4338