Top command meaning

VIRT：virtual memory usage  Virtual memory 
1、 process “ Needed ” Virtual memory size , Including libraries used by processes 、 Code 、 Data etc. 
2、 If the process applies 100m Of memory , But actually only 10m, Then it will grow 100m, Not the actual amount of usage 

RES：resident memory usage  memory-resident 
1、 The memory size currently used by the process , But does not include swap out
2、 Contains shares from other processes 
3、 If you apply 100m Of memory , The actual use 10m, It only grows 10m, And VIRT contrary 
4、 About the memory occupied by the library , It only counts the memory size of the loaded library file 

SHR：shared memory  Shared memory 
1、 In addition to the shared memory of its own processes , Also includes shared memory for other processes 
2、 Although the process only uses a few shared library functions , But it contains the size of the entire shared library 
3、 The formula to calculate the physical memory occupied by a process ：RES – SHR
4、swap out after , It will come down 

DATA
1、 Memory occupied by data . If top Did not show , Press f The key can be displayed .
2、 The data required by the real program is null