Matthew Pickering authored Mar 04, 2021 and Marge Bot committed Mar 08, 2021

The way in which allocatePinned took blocks out of the nursery was
leading to horrible fragmentation in some workloads.

The strategy now is that a separate free block list is reserved for each
capability and blocks are taken from there. When it's empty the global
SM lock is taken and a fresh block of size PINNED_EMPTY_SIZE is allocated.

Fixes #19481