[ale] top and SWAP

[John Wells]

Guys,

Would like some help in clarifying the SWAP column under top (you might have to add it to your view). For example, currently I see:

Tasks: 147 total,   4 running, 143 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.2%us,  0.1%sy,  0.0%ni, 99.1%id,  0.0%wa,  0.0%hi,  0.6%si,  0.0%st
Mem:   2074688k total,  1810620k used,   264068k free,   462408k buffers
Swap:  4104568k total,        0k used,  4104568k free,   585468k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  SWAP COMMAND       
10362 wellsj    23   0  851m 222m  27m S    0 11.0   0:44.24 629m java          
 8822 wellsj    18   0  647m  20m 6288 S    0  1.0   0:01.09 627m java          
 6895 www-data  24   0  225m 2304 1004 S    0  0.1   0:00.00 223m apache2       
 6897 www-data  23   0  225m 2308 1008 S    0  0.1   0:00.00 223m apache2       
 7093 wellsj    15   0  153m  30m  15m R    0  1.5   0:10.54 122m gnome-panel   
 7394 wellsj    15   0  334m 211m  23m S    0 10.5   7:58.76 122m firefox-bin   
 9809 wellsj    15   0  158m  51m  25m S    0  2.5   0:10.71 106m epiphany      
 6452 mysql     25   0  124m  20m 5012 S    0  1.0   0:00.19 104m mysqld        
 7099 wellsj    18   0 87028  18m  14m S    0  0.9   0:08.65  66m nautilus      
 7231 wellsj    15   0 63340 8708 7056 S    0  0.4   0:00.16  53m trashapplet   
 7277 wellsj    16   0 65776  11m 9220 S    0  0.6   0:00.33  52m gweather-apple
 7184 wellsj    15   0 58296 6368 5120 S    0  0.3   0:00.08  50m evolution-data
 7444 wellsj    15   0 69272  20m  10m S    0  1.0   0:03.53  47m gnome-terminal


Ok, so it appears that some processes are doing some heavy swapping. But, look above...in the header section. Swap: says there's a lot available, but *none* in use? Where's all that memory in SWAP disappearing to? 

I suppose the "cached" memory might have something to do with it, but have found no good docs describing what it indicates yet. Given that, I'm hoping it's something obvious to a person with good virtual memory understanding and am off to read on Wikipedia. However, if *you* know, I'd appreciate your insight.

Thanks!
John