* sverker/ets-no-mbuf-trapping/OTP-15660:
  erts: Remove ets traversal yielding if heap fragment

Many heap fragments do no longer make the GC slow.

Even worse, we are not guaranteed that a yield will provoke a GC
removing the fragments, which might lead to a one-yield-per-bucket
scenario if the heap fragment(s) still remains after each yield.

* john/erts/OTP-20.3.8/minusminus_trapping/OTP-15371:
  Optimize operator '--' and yield on large inputs

The removal set now uses a red-black tree instead of an array on
large inputs, decreasing runtime complexity from `n*n` to
`n*log(n)`. It will also exit early when there are no more items
left in the removal set, drastically improving performance and
memory use when the items to be removed are present near the head
of the list.

This got a lot more complicated than before as the overhead of
always using a red-black tree was unacceptable when either of the
inputs were small, but this compromise has okay-to-decent
performance regardless of input size.

Co-authored-by: Dmytro Lytovchenko <dmytro.lytovchenko@erlang-solutions.com>

* sverker/erts/ets-select_replace-bug/OTP-15346:
  erts: Fix bug in ets:select_replace for bound key

which may cause following calls to ets:next or ets:prev to fail.

OTP-14942

The small sub-binary conversion trick in the GC broke this test
pretty often on some machines.

* maint-20:
  Updated OTP version
  Update release notes
  Update version numbers
  erts: Add system_flags(erts_alloc,"+M?sbct *")
  erts: Add age order first fit allocator strategies
  erts: Refactor erl_ao_firstfit_alloc
  erts: Add migration options "acnl" and "acfml"
  kernel: Add os:cmd/2 with max_size option
  erts: Add more stats for mbcs_pool
  erts: Fix alloc_SUITE:migration
  stdlib: Make ets_SUITE memory check try again
  erts: Improve carrier pool search
  erts: Improve alloc_SUITE:migration
  erts: Refactor carrier dealloc migration