Definition
Available Physical Memory
Available physical memory is the portion of RAM not currently occupied by the kernel or active processes, ready for immediate allocation.
Sufficient available memory allows the operating system to respond quickly to process demands without disk-based paging or swapping overhead.
Memory Pressure
Responses to Low Memory
When available physical memory drops below a threshold, the operating system may:
- Swap: Move an entire process image from RAM to secondary storage.
- Reclaim pages: Evict cached file data or unused pages.
- Suspend processes: Transition a process to the Suspended state to prevent further memory consumption.
Thrashing
Insufficient available memory leads to thrashing: the system spends more time moving data between RAM and disk than executing instructions.