The roll area is a memory area with a set (configurable) size that belongs to a work process. It is located in the heap of the virtual address space of the work process.
When the context of a work process changes, the data is copied from the roll area to a common resource called the roll file. To prevent repeated copying, another roll buffer is located in between that is part of the shared memory.
The roll area consists of 2 segments. The first segment, which can be set with the parameter ztta/roll_first, is assigned to the work process first as memory. If this is used up, the work process has more memory assigned to it. The amount of memory is determined by the difference between the parameters ztta/roll_area and ztta/roll_first.
For more detailed information, please see the platform-specific section under Implementation.
For technical reasons, the roll area is always the first memory that receives a work process. Only afterwards can extended memory be requested.
See also: Virtual Address Space of a Work Process