Add tcmallocAggressiveMemoryDecommit (#5650)

* add tcmallocAggressiveMemoryDecommit

* wordsmithing

* external review suggestions and clarifications

* writing review

* Update source/reference/parameters.txt

Co-authored-by: Alison Huh <[email protected]>

* Update source/reference/parameters.txt

Co-authored-by: Alison Huh <[email protected]>

* fix formatting

* final? review

* Update source/reference/parameters.txt

Co-authored-by: Alison Huh <[email protected]>

* final changes, I hope...

* fix formatting

---------

Co-authored-by: Alison Huh <[email protected]>

Author: MongoCaleb

source/reference/parameters.txt

@@ -1844,6 +1844,30 @@ General Parameters
    .. seealso: :ref:`storage-node-watchdog`
 
 
+.. parameter:: tcmallocAggressiveMemoryDecommit
+
+   *Type*: integer (``0`` or ``1`` only)
+
+   Default: 1
+
+   If you enable `tmallocAggressiveMemoryDecommit`, MongoDB:
+   
+   - releases a :term:`chunk <chunk>` of memory to system, and 
+
+   - attempts to return all neighboring free chunks. 
+   
+   A value of ``1`` enables ``tcmallocAggressiveMemoryDecommit``; 
+   ``0`` disables this parameter.
+   
+   If you enable this parameter, the system will require new memory allocations 
+   for use. Consider enabling ``tcmallocAggressiveMemoryDecommit`` 
+   only on memory-constrained systems and after pursuing other memory and 
+   performance options.
+
+   Despite the potential performance degradation when using 
+   ``tcmallocAggressiveMemoryDecommit``, it is often preferred over using 
+   :parameter:`tcmallocReleaseRate`.
+
 .. parameter:: tcmallocReleaseRate
 
    .. versionadded:: 4.2.3 
@@ -1860,6 +1884,12 @@ General Parameters
    return memory faster; decrease it to return memory slower.
    Reasonable rates are in the range [0,10]."
 
+   .. note::
+
+      Consider using :parameter:`tcmallocAggressiveMemoryDecommit` instead of 
+      :parameter:`tcmallocReleaseRate`, unless you see a significant performance 
+      degradation when using ``tcmallocAggressiveMemoryDecommit``.
+
    To modify the release rate during run time, you can use the
    :dbcommand:`setParameter` command; for example: