LinuxQuestions.org - top virt column value

Look at the following top output, it is a classic 16 GB of RAM Linux server running Red Hat Enterprise Linux 4 64 bit.

I'm a little confused by the meaning of top's VIRT column value, as for most of the java processes (JBoss) that value is little higher than the RES value, which make sense for for 2 process is it very huge: 30.1g and 52.7g.

From what I was able to find the VIRT column is the total amount of virtual memory used by a process, meaning code, data, shared libs and swapped out pages. On that simple server, I only have 16 GB RAM and 2 GB swap (default value), how can I have those big numbers ?

When I do pmap on one of those process I get the same numbers and a lot of 262136K anon pages. I was wondering what could explain that situation?

Code:

top - 16:22:50 up  6:00,  2 users,  load average: 0.30, 0.34, 0.34

Tasks: 136 total,  2 running, 134 sleeping,  0 stopped,  0 zombie

Cpu(s):  2.1% us,  2.7% sy,  0.0% ni, 95.3% id,  0.0% wa,  0.0% hi,  0.0% si

Mem:  16188436k total,  9753688k used,  6434748k free,    80992k buffers

Swap:  2096472k total,        0k used,  2096472k free,  1756028k cached



  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND

 3341 jboss    16  0 53.7g 1.6g  61m S  1.8 10.1  21:23.21 java

 3454 jboss    18  0 30.1g 1.4g  57m S  0.0  9.0  7:13.60 java

 3571 jboss    20  0 3147m 2.3g  57m S 14.7 15.1  47:42.39 java

 3641 jboss    25  0 1924m 1.0g 105m S  0.0  6.4  10:44.38 java

 3512 jboss    16  0 1758m 791m  41m S  0.3  5.0  9:15.13 java

22703 jboss    25  0 1651m 634m  40m S  0.0  4.0  1:38.63 java

 3869 jboss    17  0 1354m  86m  11m S  0.0  0.5  1:38.23 java

 3077 nscd      16  0  188m 1984 1236 S  0.0  0.0  0:01.57 nscd

 3265 root      16  0  110m 9.9m 5464 S  0.0  0.1  0:00.20 httpd

 3306 apache    16  0  110m 5688 1012 S  0.0  0.0  0:00.00 httpd

 3309 apache    16  0  110m 5684 1008 S  0.0  0.0  0:00.00 httpd