The OS Paging (Per Second) alert indicates that a memory threshold meets or exceeds the setting, due to one of the following causes:
Consistently high memory usage could cause system performance problems because of heavy disk usage and CPU load.
A high number of memory paging indicates a memory bottleneck. You should open the Memory view on the Resources tab to see how memory is being utilized on your SQL Server instance. You may need to allocate more memory to SQL Server to increase your SQL Server performance.
To enable alerting when this metric is outside its established baseline, click the Baseline Thresholds Enabled (as percentage of baseline) check box in the Alert Configuration window.