Memory overhead

Talking about computers the more the better is usual, but this is not true all the time. By example, look at the amount of memory and load in bigservr; this server has 64 gigabytes of memory but is used just 3 gigabytes, and even if there are no running processes and the CPU usage is almost zero the load average is somewhat high. In comparison, smallsrv is busier and even having used swap memory the load average is lower than in bigservr.

The management of hardware by the Linux kernel requires resources, and in order to manage a lot of memory the kernel requires ... a lot of memory structures. Therefore, if you aren't going to use a lot of memory it would be better (and cheaper) to install just the memory you need.

myuser@bigservr> top

top - 08:50:32 up 6 days, 13:00,  4 users,  load average: 0.71, 0.74, 0.66
Tasks: 272 total,   1 running, 271 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.8%us,  0.1%sy,  0.0%ni, 99.1%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  65791000k total,  3227812k used, 62563188k free,   309716k buffers
Swap:  5406712k total,        0k used,  5406712k free,  2649252k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                      
10768 root      15   0 16420 2456 2124 S  0.3  0.0   0:39.00 cmaeventd                                                                                    
22241 myuser    15   0  2336 1136  800 R  0.3  0.0   0:01.14 top                                                                                          
    1 root      15   0  2072  616  532 S  0.0  0.0   0:08.29 init                                                                                         
    2 root      RT  -5     0    0    0 S  0.0  0.0   0:01.17 migration/0                                                                                  
    3 root      39  19     0    0    0 S  0.0  0.0   0:00.00 ksoftirqd/0                                                                                  
    4 root      RT  -5     0    0    0 S  0.0  0.0   0:00.00 watchdog/0                                                                                   
    5 root      RT  -5     0    0    0 S  0.0  0.0   0:01.44 migration/1                                                                                  
    6 root      34  19     0    0    0 S  0.0  0.0   0:00.07 ksoftirqd/1                                                                                  
    7 root      RT  -5     0    0    0 S  0.0  0.0   0:00.00 watchdog/1                                                                                   
    8 root      RT  -5     0    0    0 S  0.0  0.0   0:01.01 migration/2                                                                                  
    9 root      34  19     0    0    0 S  0.0  0.0   0:00.02 ksoftirqd/2                                                                                  
   10 root      RT  -5     0    0    0 S  0.0  0.0   0:00.00 watchdog/2                                                                                   
   11 root      RT  -5     0    0    0 S  0.0  0.0   0:01.72 migration/3                                                                                  

root@smallsrv:~# top

top - 08:51:20 up 29 min,  6 users,  load average: 0.16, 0.21, 0.46
Tasks: 184 total,   2 running, 182 sleeping,   0 stopped,   0 zombie
Cpu(s):  7.0%us, 12.3%sy,  0.0%ni, 79.3%id,  1.3%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   1016864k total,   987644k used,    29220k free,    44384k buffers
Swap:  2980016k total,   204780k used,  2775236k free,   604592k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND           
 2599 myuser    10 -10  271m 186m 177m S  9.6 18.8   2:55.94 vmware-vmx        
 2377 myuser    20   0  388m 103m  19m S  4.3 10.4   0:50.69 firefox-bin       
 1030 root      20   0  105m  20m 9428 S  3.0  2.1   1:00.57 Xorg              
 2435 myuser    20   0 73624  13m 9.9m S  1.3  1.4   0:15.40 plugin-containe   
 3479 root      20   0  2472 1196  880 R  0.7  0.1   0:00.06 top               
   16 root      15  -5     0    0    0 S  0.3  0.0   0:00.39 ata/0             
 2028 myuser    20   0  110m  10m 5832 S  0.3  1.1   0:12.17 compiz.real       
 2206 myuser    20   0  113m  11m 8324 S  0.3  1.2   0:04.71 gnome-terminal    
 2938 root       0 -20     0    0    0 R  0.3  0.0   0:08.41 vmware-rtc        
    1 root      20   0  2532 1420 1096 S  0.0  0.1   0:00.98 init              
    2 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 kthreadd          
    3 root      RT  -5     0    0    0 S  0.0  0.0   0:00.00 migration/0       
    4 root      15  -5     0    0    0 S  0.0  0.0   0:00.09 ksoftirqd/0       
    5 root      RT  -5     0    0    0 S  0.0  0.0   0:00.00 watchdog/0        
    6 root      15  -5     0    0    0 S  0.0  0.0   0:00.02 events/0          
    7 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 cpuset            
    8 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 khelper