abap/heap_area_dia: Heap Memory Limit for Dialog Work Processes 
This quota restricts the amount of heap memory (Private Memory) that an SAP dialog work process can allocate. This ensures that there is enough swap space available.
Note
Local memory is hardly needed any more with modern 64 bit platforms, as the memory requirement can be satisfied by the SAP Extended Memory.
Integration
The graphic below shows the relationship with abap/heaplimit.
If the value of abap/heaplimit has been reached, the work process is restarted after the dialog step has ended. If the consumption of heap memory exceeds the quota abap/heaparea_(non)dia, the user context being executed at this time is cancelled before it can be completed.
You can use this quota to prevent one single dialog work process (user context) from filling the entire heap memory of the application server.
The work processes of an application server can allocate only so much heap memory as specified in parameter abap/heap_area_total. The limit specified in the parameter refers to the combined heap memory usage of all work processes for an application server.
Activities
The value is specified in bytes.
The default value is platform-specific and is determined dynamically. This is the Defaultwert specified in transaction RZ11. This value should not normally be changed.
Note
Ensure that the value is high enough to fulfill all the regualr memory requirements, but is not so high that the work process runs up against the swap space limit of the operating system. See the graphic in abap/heaplimit: Work Process Restart..