Most of the lsa gory details are hidden in utils/logalloc.cc. That
includes the actual implementation of a lsa region: region_impl.
However, there is code in the hot path that often accesses the
_reclaiming_enabled member as well as its base class
allocation_strategy.
In order to optimise those accesses another class is introduced:
basic_region_impl that inherits from allocation_strategy and is a base
of region_impl. It is defined in utils/logalloc.hh so that it is
publicly visible and its member functions are inlineable from anywhere
in the code. This class is supposed to be as small as possible, but
contain all members and functions that are accessed from the fast path
and should be inlined.
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