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Why these processes use swap

User51642 Yong Huang
User51642 Yong Huang Member Posts: 160 Bronze Badge

On RHEL 7.9 server with 256 GB memory, I see some swap usage:

myhost:~# free
             total       used       free     shared buff/cache  available
Mem:     263975272  168050976    1336696    2540912   94587600   91825580
Swap:     16678908     504832   16174076

It's not a concern and there's no performance issue. But I'm curious to see what processes are using swap. Here's my way to find them:

myhost:~# grep VmSwap /proc/[1-9]*/status | grep -v ' 0 kB$' | sort -nk2 | tail
/proc/11980/status:VmSwap:         5580 kB
/proc/10417/status:VmSwap:        10236 kB
/proc/10234/status:VmSwap:        11640 kB
/proc/1669/status:VmSwap:         16464 kB
/proc/16410/status:VmSwap:        18264 kB
/proc/14695/status:VmSwap:        31716 kB
/proc/3859/status:VmSwap:         56380 kB
/proc/1371/status:VmSwap:         65708 kB
/proc/3863/status:VmSwap:         73824 kB
/proc/3867/status:VmSwap:         75936 kB
myhost:~# ps -opid,rss,cmd -p3867,3863,14695
 PID  RSS CMD
 3863 1756 /u01/app/oracle/goldengate/bin/recvsrvr --config /ogg/sm/var/temp/ogg_ma_fscqae-recvsrvr-config.dat --force --quiet
 3867 30588 /u01/app/oracle/goldengate/bin/distsrvr --config /ogg/sm/var/temp/ogg_ma_fscqae-distsrvr-config.dat --force --quiet
14695 128676 rmiregistry 10100

I picked a few to see. Most are our GoldenGate processes. But none of them are using a lot of real memory (resident set memory under column RSS). In fact, the biggest memory hoggers are our Peoplesoft processes that happen to be running on this box:

myhost:~# ps -opid,rss,cmd -p24387
 PID  RSS CMD
24387 5538388 PSAPPSRV -C dom=FSCQAE_204061 -g 99 -i 8 -u myhost -U /apps/fsc/pt857/qae/appserv/FSCQAE/LOGS/TUXLOG -m 0 -o ./

and yet those processes do not use swap (nor HugePages). My question is, what caused some processes such as those GoldenGate processes to use swap? Did they demand a huge amount of memory at some point in time?

Best Answer

  • Nik
    Nik Blocked Member Posts: 2,879 Bronze Crown
    Answer ✓

    Hi.

    It's not process choice use or not swap. Operating System manage this process.

    OS try use all free memory for FS cache.

    In case some process write some information at memory but long time not use this information and you have active work with files, OS can put this information on swap device for allocate more memory for FS cache.

    You can manage this process.

    Read about /proc/sys/vm/swappiness

    Regards,

    Nik

Answers

  • Nik
    Nik Blocked Member Posts: 2,879 Bronze Crown
    Answer ✓

    Hi.

    It's not process choice use or not swap. Operating System manage this process.

    OS try use all free memory for FS cache.

    In case some process write some information at memory but long time not use this information and you have active work with files, OS can put this information on swap device for allocate more memory for FS cache.

    You can manage this process.

    Read about /proc/sys/vm/swappiness

    Regards,

    Nik