Swapping is seen as a nasty effect on modern systems. When the systems performance goes down there is a bunch of scenarios where significant swapping is observed. Unfortunately a root cause is hard to identify. Those processes which get part of their memory paged out are not those which create memory pressure. Also the memory demand can be quite short lived and therefore hard to observe in sample based monitoring.
Still sometimes I'd like to see at least which processes are affected from paged out memory. If they don't need to access this memory for whatever reason, that doesn't mean any problem at all. But of course, we mostly have to look at those systems which show any kind of issue.
Unfortunately I did not find any tool which shows me a useful number of memory paged out per process, so I had to come up with my own.
My simple script checks all processes /proc/pid/status "file". There the line with name should help out:
VmSwap Swapped-out virtual memory size by anonymous
private pages; shmem swap usage is not included
(since Linux 2.6.34). This value is inaccurate;
see /proc/pid/statm above.The warning doesn't sound promising, but the explanation given for statm is somehow acceptable (for me):
Some of these values are inaccurate because of a kernel- internal scalability optimization. If accurate values are required, use /proc/pid/smaps or /proc/pid/smaps_rollup instead, which are much slower but provide accurate, detailed information.
For my purpose that's good enough! I need an overview and doesn't want to put even more load on a system by parsing all smaps entries.
So my script is quite short:
(echo " SWAP PID USER PROGRAM"
echo
ps -ewo pid,user,comm \
| while read -r pid user cmd ; do
VmSwap=$(awk ' /VmSwap/ { print $2 } ' /proc/${pid}/status 2>/dev/null)
if [ ${VmSwap:-0} -gt 0 ]; then
printf "%12d kB %7d %10s %s \n" "${VmSwap:-0}" "$pid" "$user" "$cmd"
fi
done | sort -n
echo
echo " SWAP PID USER PROGRAM"
echo )
SWAP PID USER PROGRAM
55640 kB 51304 root crsd.bin
59068 kB 385709 oracle ora_lgwr_zzz1
60672 kB 94092 oracle ora_lg04_zzz3
97668 kB 396323 root java
115136 kB 385731 oracle ora_lg00_zzz1
119728 kB 385879 oracle ora_mmon_zzz1
121484 kB 385841 oracle ora_lg04_zzz1
185296 kB 14656 root ohasd.bin
431344 kB 53850 grid java
564416 kB 19273 oracle java
SWAP PID USER PROGRAM
Unfortunately, the documentation is slightly unspecific regarding the requirements: glibc 2.14 is met, but in my system only 64 bit by default. 