free / top difference. Does free show virtual memory?

Question

free -m shows me the following in my system:

             total       used       free     shared    buffers     cached
Mem:          3954       3842        111          0        248       2585
-/+ buffers/cache:       1008       2945
Swap:         3811          4       3807

So memory looks pretty used up, but top sorted by memory shows the following top-processes:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                                                              
 8891 minecraf  20   0 2374m 277m 9.9m S    1  7.0   0:12.21 java                                                                                                                                                                  
 8704 root      39  19 2802m 272m  11m S    0  6.9   0:28.73 java      

The virtual memory used by java seems to be huge, but i learned on the internet that that's not a problem. So i guess my question is: Why does free show the virtual memory, if it's not that meaningful?

Solution

The "Mem" line of free doesn't show virtual memory usage, it shows physical memory usage.

The "RES" (for resident) and "%MEM" columns from top shows you the same: the physical memory being used by each process.

free does show you the available and used swap space, and top has its "VIRT" column, both of which can be important. Roughly, swap space plus physical memory gives you your total possible virtual memory space. Get up to that limit and you'll start getting processes killed or unable to allocate memory and things will be bad.

Comments

[clerksx]

Just because this particular information might not be useful for your particular scenario, it doesn't mean that it isn't useful in other situations.

[Fabian Zeindl]

Then i don't get why my memory is almost used up. Those two processes are at the top, beneath it all other processes use < 5MB res memory.

[John Flatness]

Yes, the "Mem" and "+/- buffers/cache" lines can be a little confusing, but there's another question here that has some explanation. For what you're probably expecting for free memory, I'd look at the "free" column of the "+/-" row.

[CMCDragonkai]

Is buffers/cache part counted as part of virtual memory or resident memory?