Linux: find out what process is using all the RAM?

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Problem :

Before actually asking, just to be clear: yes, I know about disk cache, and no, it is not my case 🙂 Sorry, for this preamble 🙂

I’m using CentOS 5. Every application in the system is swapping heavily, and the system is very slow. When I do free -m, here is what I got:

             total       used       free     shared    buffers     cached
Mem:          3952       3929         22          0          1         18
-/+ buffers/cache:       3909         42
Swap:        16383         46      16337

So, I actually have only 42 Mb to use! As far as I understand, -/+ buffers/cache actually doesn’t count the disk cache, so I indeed only have 42 Mb, right? I thought, I might be wrong, so I tried to switch off the disk caching and it had no effect – the picture remained the same.

So, I decided to find out who is using all my RAM, and I used top for that. But, apparently, it reports that no process is using my RAM. The only process in my top is MySQL, but it is using 0.1% of RAM and 400Mb of swap. Same picture when I try to run other services or applications – all go in swap, top shows that MEM is not used (0.1% maximum for any process).

top - 15:09:00 up  2:09,  2 users,  load average: 0.02, 0.16, 0.11
Tasks: 112 total,   1 running, 111 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   4046868k total,  4001368k used,    45500k free,      748k buffers
Swap: 16777208k total,    68840k used, 16708368k free,    16632k cached

 3214 ntp       15   0 23412 5044 3916 S  0.0  0.1   0:00.00  17m ntpd
 2319 root       5 -10 12648 4460 3184 S  0.0  0.1   0:00.00 8188 iscsid
 2168 root      RT   0 22120 3692 2848 S  0.0  0.1   0:00.00  17m multipathd
 5113 mysql     18   0  474m 2356  856 S  0.0  0.1   0:00.11 472m mysqld
 4106 root      34  19  251m 1944 1360 S  0.0  0.0   0:00.11 249m yum-updatesd
 4109 root      15   0 90152 1904 1772 S  0.0  0.0   0:00.18  86m sshd
 5175 root      15   0 90156 1896 1772 S  0.0  0.0   0:00.02  86m sshd

Restart doesn’t help, and, by they way is very slow, which I wouldn’t normally expect on this machine (4 cores, 4Gb RAM, RAID1).

So, with that – I’m pretty sure that this is not a disk cache, who is using the RAM, because normally it should have been reduced and let other processes to use RAM, rather then go to swap.

So, finally, the question is – if someone has any ideas how to find out what process is actually using the memory so heavily?

Solution :

On Linux in the top process you can press < key to shift the output display sort left. By default it is sorted by the %CPU so if you press the key 4 times you will sort it by VIRT which is virtual memory size giving you your answer.

Another way to do this is:

ps -e -o pid,vsz,comm= | sort -n -k 2

should give you and output sorted by processes virtual size.

Here’s the long version:

ps --everyone --format=pid,vsz,comm= | sort --numeric-sort --key=2

Show the processes memory in megabytes and the process path.

ps aux  | awk '{print $6/1024 " MBtt" $11}'  | sort -n

Just a side note on a server showing the same symptoms but still showing memory exhaustion. What ended up finding was a sysctl.conf from a box with 32 GB of RAM and setup for a DB with huge pages configured to 12000. This box only has 2 GB of RAM so it was assigning all free RAM to the huge pages (only 960 of them). Setting huge pages to 10, as none were used anyway, freed up all of the memory.

A quick check of /proc/meminfo to look for the HugePages_ settings can be a good start to troubleshooting at least one unexpected memory hog.

Make a script called with content:

ps -eo rss,pid,user,command | sort -rn | head -$1 | awk '{ hr[1024**2]="GB"; hr[1024]="MB";
 for (x=1024**3; x>=1024; x/=1024) {
 if ($1>=x) { printf ("%-6.2f %s ", $1/x, hr[x]); break }
 } } { printf ("%-6s %-10s ", $2, $3) }
 { for ( x=4 ; x<=NF ; x++ ) { printf ("%s ",$x) } print ("n") }

Make it executable with chmod +x and call it like this ./ 10 (10 => show max 10 lines)

Output Example:

5.54   GB 12783  mysql      /usr/sbin/mysqld

1.02   GB 27582  root       /usr/local/cpanel/3rdparty/bin/clamd

131.82 MB 1128   company+   /opt/cpanel/ea-php73/root/usr/bin/php /home/companyde/ queue:consumers:start inventory.mass.update --single-thread --max-messages=10000

131.21 MB 1095   company+   /opt/cpanel/ea-php73/root/usr/bin/php /home/companyde/ queue:consumers:start product_action_attribute.update --single-thread --max-messages=10000

131.19 MB 1102   company+   /opt/cpanel/ea-php73/root/usr/bin/php /home/companyde/ queue:consumers:start --single-thread --max-messages=10000

130.80 MB 1115   company+   /opt/cpanel/ea-php73/root/usr/bin/php /home/companyde/ queue:consumers:start exportProcessor --single-thread --max-messages=10000

130.69 MB 1134   company+   /opt/cpanel/ea-php73/root/usr/bin/php /home/companyde/ queue:consumers:start inventory.reservations.update --single-thread --max-messages=10000

130.69 MB 1131   company+   /opt/cpanel/ea-php73/root/usr/bin/php /home/companyde/ queue:consumers:start inventory.reservations.cleanup --single-thread --max-messages=10000

130.69 MB 1107   company+   /opt/cpanel/ea-php73/root/usr/bin/php /home/companyde/ queue:consumers:start codegeneratorProcessor --single-thread --max-messages=10000

130.58 MB 1120   company+   /opt/cpanel/ea-php73/root/usr/bin/php /home/companyde/ queue:consumers:start inventory.source.items.cleanup --single-thread --max-messages=10000

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