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MTSS: multi task stack sharing for embedded systems

Out-of-memory errors are a serious source of unreliability in most embedded systems [22]. Applications run out of main memory because of the frequent difficulty of estimating the memory requirement before deployment, either because it depends on input data, or because certain language features prevent estimation. The typical lack of disks and virtual memory in embedded systems has a serious consequence when an out-of-memory error occurs. Since there is no swap space for the application to grow into, the system crashes if its memory footprint is exceeded by even one byte.This work improves system reliability for multi-tasking embedded systems by proposing MTSS, a multi-task stack sharing technique, that grows the stack of a particular task into other tasks in the system after it has overflown its bounds. This technique can avoid the out-of-memory error if the extra space recovered is enough to complete execution. Experiments show that MTSS, on an average, is able to recover 47% of the stack space allocated to the overflowing task in the free space of other tasks. Therefore, even if we underestimate the stack size of a particular task by 47% on an average, it will still run to completion by reusing stack in other task's stack.Alternatively, MTSS can also be used for decreasing the physical memory for an embedded system by reducing the initial memory allocated to each of the tasks and recovering the deficit by sharing stack with other tasks. Results show that MTSS used in this way can be used to reduce the memory required in multi-tasking embedded systems by 18% on an average, thus reducing the memory cost of the system. MTSS also offers good real time guarantees, since it uses a paging system that never incurs an episodic increase in run-time.The overheads of MTSS are extremely low: the run-time and code size overheads are 1.8% and 2.6% on an average, making it a feasible method for increasing system reliability and reducing the memory footprint of embedded systems.