This read-only integer reports the amount of memory, in kB/s, being swapped in from swap files, which may include pages retrieved due to page faults or other data. An admin watches for sustained nonzero values here as a direct sign of memory pressure causing active swapping, which typically degrades application performance. For example, a persistent swap-in rate observed during business hours would prompt an admin to investigate which process's memory footprint is forcing the system to swap.