Investigating Unexpected Swap Usage in a Java Service on an 8 GB Server
Despite allocating a 6 GB heap to a Java service on an 8 GB server—leaving roughly 1.4 GB for the OS and monitoring—the system still swaps heavily, because the kernel’s non‑heap memory, page cache, and overcommit handling consume the remaining RAM, causing GC pauses and severe JVM stalls.
On servers equipped with 8 GB of physical memory, a Java service is configured with a 6 GB JVM heap, while a monitoring process consumes roughly 600 MB and the Linux operating system itself uses about 800 MB. Superficially, the memory allocation appears sufficient for the workload.
In practice, however, the system experiences extensive swap usage, as illustrated in the accompanying screenshot. The simultaneous occurrence of swap activity and garbage collection (GC) leads to severe JVM stalls, prompting the question: where is the memory actually going?
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