8.2.2.2 Monitoring Memory Usage

The sar -r command reports memory utilization statistics, including %memused, which is the percentage of physical memory in use.

sar -B reports memory paging statistics, including pgscank/s, which is the number of memory pages scanned by the kswapd daemon per second, and pgscand/s, which is the number of memory pages scanned directly per second.

sar -W reports swapping statistics, including pswpin/s and pswpout/s, which are the numbers of pages per second swapped in and out per second.

If %memused is near 100% and the scan rate is continuously over 200 pages per second, the system has a memory shortage.

Once a system runs out of real or physical memory and starts using swap space, its performance deteriorates dramatically. If you run out of swap space, your programs or the entire operating system are likely to crash. If free or top indicate that little swap space remains available, this is also an indication you are running low on memory.

The output from the dmesg command might include notification of any problems with physical memory that were detected at boot time.