CommittedAS

CommittedAS, short for Committed Address Space, is a memory-management concept used by operating systems to describe the portion of virtual address space that has been allocated for use and is guaranteed to be backed by physical memory or swap (or other backing store). It represents the kernel’s commitment to provide backing storage for memory allocations, even if the pages are not currently resident in RAM.

The concept sits between total virtual address space and actual physical memory usage. An application may allocate or reserve address space without immediately consuming physical memory, and CommittedAS may grow as allocations are made and promises to back those allocations are recorded. Because some of the committed space may be backed by swap or other storage, CommittedAS can exceed the amount of RAM currently in use, but it is still constrained by the system’s overall backing capacity.

Measurement and reporting: CommittedAS is reported by the operating system as part of memory accounting. On Linux, a closely related metric appears in the kernel’s memory statistics as Committed_AS and is typically shown in kilobytes via /proc/meminfo. In Windows, a similar concept is tracked as the commit charge or commit size, which tools such as Task Manager report under memory usage.

Relation to other metrics: Virtual memory size (VMS) reflects the total address space allocated to a process, while resident set size (RSS) indicates pages actually present in physical RAM. CommittedAS focuses on the kernel’s guarantee of backing storage for allocated address space and is a key factor in assessing memory pressure and potential overcommit or out-of-memory conditions. Commit limits bound the maximum permissible CommittedAS based on physical RAM and swap.