Definition
Available Physical Memory
Available physical memory refers to the portion of the system’s random-access memory (RAM) that is not currently occupied by the kernel or any active processes. This memory is immediately ready for allocation to new or existing processes.
Maintaining a sufficient amount of available memory is critical for ensuring that the operating system can respond quickly to process demands and avoid the high overhead of disk-based paging or swapping.
Resource Pressure
When the amount of available physical memory drops below a certain threshold, the operating system may take the following actions:
- Swapping: Moving an entire process image from RAM to secondary storage.
- Page Reclamation: Evicting cached file data or rarely used memory pages.
- Suspension: Moving a process to a Suspended state to prevent it from consuming further memory.
Insufficient available memory leads to thrashing, where the system spends more time moving data between RAM and disk than executing instructions.