z/OS MVS Initialization and Tuning Guide
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Large frame area (LFAREA)

z/OS MVS Initialization and Tuning Guide
SA23-1379-02

The large frame area is used for the fixed 1 MB large pages and fixed 2 GB large pages. Using large pages can improve performance for some applications by reducing the overhead of dynamic address translation. This is achieved by each large page requiring only one entry in the Translation Look-aside Buffer (TLB), as compared to the larger number of entries required for an equivalent number of 4 KB pages. A single TLB entry improves TLB coverage for exploiters of large pages by increasing the hit rate and decreasing the number of TLB misses that an application incurs.

Attention: Large pages are a performance improvement feature for some cases—switching to large pages is not recommended for all workloads.

Large pages provide performance value to a select set of applications that can generally be characterized as memory access-intensive and long-running. These applications meet the following criteria:

  1. They must reference large ranges of memory.
  2. They tend to exhaust the private storage areas available within the 2 GB address space (such as the IBM® WebSphere® application), or they use private storage above the 2 GB address space (such as IBM DB2® software).

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