release candidate for legion-21.12.0

CHANGES.txt

@@ -1,14 +1,23 @@
 This file lists the major changes as they appear in the stable branch.  No
 attempt is made to keep this list accurate for the master branch.
 
-Version 21.12.0 (December ??, 2021)
+Version 21.12.0 (December 31, 2021)
   * Realm
      - Performance improvements for multi-dimensional copies, especially
         inter-process transfers
      - Support for loading CUDA driver (if present) at runtime instead of
         link time, allowing same binary to be used on systems with and without
         CUDA-capable GPUs (enabled with -DLegion_CUDA_DYNAMIC_LOAD=ON in
         cmake build)
+     - A separate `Memory` is now created per process for external (system)
+        memory instances.  This memory has no capacity for creating instances
+        and can confuse applications or Legion mappers that assume exactly
+        one Memory of kind `SYSTEM_MEM` exists.  Old behavior can be obtained
+        with `-ll:ext_sysmem 0`, but this can fail for configurations that
+        register system memory with the network and/or GPUs
+     - The `MemoryQuery` now supports a `has_capacity` predicate to restrict
+        results to just memories with sufficient total (not current!) capacity
+        to allocate an instance of a specified size
   * Build
      - Cmake allows control of max nodes (-DLegion_MAX_NUM_NODES=...) and
         max processors/node (-DLegion_MAX_NUM_PROCS=...) supported by