rdisp/ROLL_SHM: Roll Buffer Size
This value specifies the size of the roll buffer in 8 KB blocks.
The roll buffer functions as the cache for the roll file. For a fast change of context to occur, the roll areas of all user contexts should find space in the roll buffer (approximately 1 MB for each user).
Goal:
Minimum time for a context change
Buffered data is in the shared memory; accessing this data here is much faster than accessing a file.
For technical reasons, the roll buffer size must be at least 10% of the roll file size (parameter