Look at process memory usage under linux for an in depth understanding

Dynamically view a process's memory usage

1 , top The command 
top -d 1 -p pid [,pid ...] // Set to delay 1s The default is delay 3s
 If you want to sort by memory usage, you can shift + m ( Sort by memory usage ) 

Statically view a process's memory usage

1 , pmap The command 
pmap pid
2 , ps The command 
ps aux|grep process_name
3 And check /proc/process_id/ subfolder status file 
Name:   php
State:  R (running)
SleepAVG:       0%
Tgid:   21574
Pid:    21574
PPid:   10005
TracerPid:      0
Uid:    1000    1000    1000    1000
Gid:    100     100     100     100
FDSize: 256
Groups: 16 100 
VmPeak:   161740 kB
VmSize:   161740 kB
VmLck:         0 kB
VmHWM:    107144 kB
VmRSS:    107144 kB
VmData:   106192 kB
VmStk:        84 kB
VmExe:      5588 kB
VmLib:      7884 kB
VmPTE:       268 kB
Threads:        1
SigQ:   0/69632
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000001000
SigCgt: 00000001818040a7
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
Cpus_allowed:   00000000,00000000,00000000,0000000f
Mems_allowed:   1
 The size of the task virtual address space  VmSize
 The size of the physical memory being used by the application  VmRSS