Friday, 26 April 2013

Paging Space Administration -AIX


All these questions about paging space will be answered in this very particular post.
1) What is Paging Space?
In a system, there are multiple processes running. For a new process to be actively running, the process should be loaded into the OS memory. Once the process is loaded, it is then assigned number of 4 KB units called page frames.
Keeping this in view, more number of additional processes is loaded into the memory with each process assigned 4 KB areas. But when the processes are overloaded and the memory is full, OS scans memory to trace frames that are least recently used. When such a frame is discovered, 4 KB block or page of disk space is allocated and the data from least active frame is moved to area on the disk. This area on disk is called Paging Space.
2) What is Page-in & Page-out?
If the paged out information for the least active process is needed back into the memory, the page is retrieved from the disk and brought back into the memory. This is called page-in.
Similarly, when the least active frame is moved out from the memory on to the disk, the process is called page-out.
3) What is thrashing?
If the OS is loaded with many active processes and there is no further real memory available to load additional active processes, the OS goes into the constant state of paging called thrashing as no additional real memory is available to load a new process into the memory.
Increasing the amount of paging Space will be of no benefit because the processes involved are all active and thrashing is the result of not enough real memory.

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