Large memory systems contain enough memory to cache thousands of 10-Mbyte files without making severe memory demands. However, this situation is highly application dependent.
The goal of the smallfile and freebehind parameters is to reuse cached information, without causing memory shortfalls by caching too much.
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Increase smallfile if an application does sequential reads on medium-sized files and can most likely benefit from buffering, and the system is not otherwise under pressure for free memory. Medium-sized files are 32 Kbytes to 2 Gbytes in size.