Dynamic Capacity is a feature of a CXL memory device that allows memory capacity to change dynamically without the need for resetting the device. A DCD is a CXL memory device that implements Dynamic Capacity. Unlike a traditional DPA range that a CXL memory device might support, a Dynamic Capacity DPA range is subdivided into 1 to 8 DC Regions, each of which is subdivided by the DCD into a number of fixed-size blocks, referred to as DC blocks. The host software is expected to program the maximum potential capacity utilizing one or more HDM decoders to span the entire DPA range of all configured regions. The DCD controls the allocation of these DC blocks to the host and utilizes events to signal the host when changes to the allocation of these DC blocks occurs. The DCD communicates the state of these DC blocks through an Extent List that describes the starting DPA and length of all DC blocks the host can access. The Extent List does not contain extents that are still pending acceptance from the host via the Add Dynamic Capacity Response command (see Section 8.2.9.9.9.3). Similarly, the Extent List does contain extents that are still pending release acceptance from the host via the Release Dynamic Capacity command (see Section 8.2.9.9.9.4).
The next figure is the DCD illustration from Astera Labs.
