memory pressure
also: memory contention, memory starvation
Memory pressure occurs when the system's available RAM is scarce relative to demand, forcing the kernel to free up memory through swapping, page eviction, or killing processes.
Memory pressure is a state where the Linux kernel must actively work to free up physical memory because running processes are requesting more RAM than is currently available. The kernel responds by writing inactive memory pages to disk (swapping), evicting file cache, or in severe cases, invoking the Out-Of-Memory (OOM) killer to terminate processes.
Common indicators of memory pressure include high swap usage, increased disk I/O, sluggish system response, and elevated CPU time spent in the kernel's memory management routines. You can observe memory pressure using tools like free, vmstat, or /proc/pressure/memory on newer kernels.
For example, if a system has 8GB of RAM and applications collectively try to use 10GB, the kernel experiences memory pressure and must decide which pages to swap out. Sustained high memory pressure degrades performance since disk access is thousands of times slower than RAM access.