ps:

USER      PID    %CPU %MEM   VSZ   RSS  TTY  STAT  START  TIME  COMMAND 
root          4238     0.0        0.0     52396  352   pts/0    S       21:29    0:00   ./prog

VSZ指的是进程内存空间的大小，这里是52396KB； 
RSS指的是驻留物理内存中的内存大小，这里是352KB。

一般系统管理员知道VSZ并不代表进程真正用到的内存，因为有些空间会仅在页表中挂个名，也就是说只是虚拟存在着，只有真正用到的时候内核才会把虚拟页面和真正的物理页面映射起来。比如，prog.c中用malloc()分配的32MB内存，由于程序中并没有用到这些内存，没有物理内存被分配，也就不应算到进程的帐上。

进程的内存使用情况比较复杂，这是因为： 

• 进程所申请的内存不一定真正会被用到
• 真正用到了的内存也不一定是只有该进程自己在用 (比如动态共享库)

有效的实际使用内存 = 该进程独占的内存 + 共享的内存A /共享A的进程数目 + 共享的内存B /共享B的进程数目 + ...

free -m
total(96679)表示系统中物理内存总量。 
used(1631)表示已经分配的物理内存。 
free(95048)表示尚未分配的物理内存。 
shared(0)表示共享内存。 
buffers(196)表示分配给用作buffer的内存。 
cached(283)表示分配给用作cached的内存。 
第二行： 
-buffers/cache(1151): 第一行中的used - buffers - cached 
+buffer/cache(95528): 第一行中的free + buffers + cached 
说明：数据会有些许的误差，猜测是四舍五入引起的。 
-buffers/cache可以表示被进程实实在在消耗掉的内存。 
+buffers/cache可以表示还可以分配的内存大小。因为buffers/cache还可以被压缩。 
buffers和cache的区别： 
A buffer is something that has yet to be “written” to disk. A cache is something that has been “read” from the disk and stored for later use. 
第三行： 
交换区。当内存不够用的时候，系统会选择合适的进程，将其交换到swap区，把它占用的内存重新分配给其他进程。第三行表示swap区的大小和已经被使用掉的空间。

maps

Each row in /proc/$PID/maps describes a region of contiguous virtual memory in a process or thread. Each row has the following fields:

address           perms offset  dev   inode   pathname

08048000-08056000 r-xp 00000000 03:0c 64593   /usr/sbin/gpm

• address - This is the starting and ending address of the region in the process's address space
• permissions - This describes how pages in the region can be accessed. There are four different permissions: read, write, execute, and shared. If read/write/execute are disabled, a '-' will appear instead of the 'r'/'w'/'x'. If a region is not shared, it is private, so a 'p' will appear instead of an 's'. If the process attempts to access memory in a way that is not permitted, a segmentation fault is generated. Permissions can be changed using the mprotect system call.
• offset - If the region was mapped from a file (using mmap), this is the offset in the file where the mapping begins. If the memory was not mapped from a file, it's just 0.
• device - If the region was mapped from a file, this is the major and minor device number (in hex) where the file lives.
• inode - If the region was mapped from a file, this is the file number.
• pathname - If the region was mapped from a file, this is the name of the file. This field is blank for anonymous mapped regions. There are also special regions with names like [heap], [stack], or [vdso]. [vdso] stands for virtual dynamic shared object. It's used by system calls to switch to kernel mode. Here's a good article about it.

You might notice a lot of anonymous regions. These are usually created by mmap but are not attached to any file. They are used for a lot of miscellaneous things like shared memory or buffers not allocated on the heap. For instance, I think the pthread library uses anonymous mapped regions as stacks for new threads

      The format of the file is:

    address           perms offset  dev   inode       pathname

    00400000-00452000 r-xp 00000000 08:02 173521      /usr/bin/dbus-daemon

    00651000-00652000 r--p 00051000 08:02 173521      /usr/bin/dbus-daemon

    00652000-00655000 rw-p 00052000 08:02 173521      /usr/bin/dbus-daemon

    00e03000-00e24000 rw-p 00000000 00:00 0           [heap]

    00e24000-011f7000 rw-p 00000000 00:00 0           [heap]

    ...

    35b1800000-35b1820000 r-xp 00000000 08:02 135522  /usr/lib64/ld-2.15.so

    35b1a1f000-35b1a20000 r--p 0001f000 08:02 135522  /usr/lib64/ld-2.15.so

    35b1a20000-35b1a21000 rw-p 00020000 08:02 135522  /usr/lib64/ld-2.15.so

    35b1a21000-35b1a22000 rw-p 00000000 00:00 0

    35b1c00000-35b1dac000 r-xp 00000000 08:02 135870  /usr/lib64/libc-2.15.so

    35b1dac000-35b1fac000 ---p 001ac000 08:02 135870  /usr/lib64/libc-2.15.so

    35b1fac000-35b1fb0000 r--p 001ac000 08:02 135870  /usr/lib64/libc-2.15.so

    35b1fb0000-35b1fb2000 rw-p 001b0000 08:02 135870  /usr/lib64/libc-2.15.so

    ...

    f2c6ff8c000-7f2c7078c000 rw-p 00000000 00:00 0    [stack:986]

    ...

    7fffb2c0d000-7fffb2c2e000 rw-p 00000000 00:00 0   [stack]

    7fffb2d48000-7fffb2d49000 r-xp 00000000 00:00 0   [vdso]

              The address field is the address space in the process that the

              mapping occupies.  The perms field is a set of permissions:

                  r = read

                  w = write

                  x = execute

                  s = shared

                  p = private (copy on write)

              The offset field is the offset into the file/whatever; dev is

              the device (major:minor); inode is the inode on that device.

              0 indicates that no inode is associated with the memory

              region, as would be the case with BSS (uninitialized data).

              The pathname field will usually be the file that is backing

              the mapping.  For ELF files, you can easily coordinate with

              the offset field by looking at the Offset field in the ELF

              program headers (readelf -l).

              There are additional helpful pseudo-paths:

                   [stack]

                          The initial process's (also known as the main

                          thread's) stack.

                   [stack:<tid>] (since Linux 3.4)

                          A thread's stack (where the <tid> is a thread ID).

                          It corresponds to the /proc/[pid]/task/[tid]/

                          path.

                   [vdso] The virtual dynamically linked shared object.  See
vdso(7).

                   [heap] The process's heap.

              If the pathname field is blank, this is an anonymous mapping

              as obtained via mmap(2).  There is no easy way to coordinate

              this back to a process's source, short of running it through
gdb(1), strace(1), or similar.

status：

 Develop>cat /proc/24475/status

Name:    netio   可执行程序的名字

State:    R (running) 任务状态，运行/睡眠/僵死

Tgid:    24475  线程组号

Pid:    24475   进程id

PPid:    19635  父进程id

TracerPid:    0

Uid:    0    0    0    0

Gid:    0    0    0    0

FDSize:    256 该进程最大文件描述符个数

Groups:    0

VmPeak:     6330708 kB  内存使用峰值

VmSize:      268876 kB 进程虚拟地址空间大小

VmLck:           0 kB 进程锁住的物理内存大小，锁住的物理内存无法交换到硬盘

VmHWM:       16656 kB

VmRSS:       11420 kB 进程正在使用的物理内存大小

VmData:      230844 kB 进程数据段大小

VmStk:         136 kB 进程用户态栈大小

VmExe:         760 kB 进程代码段大小

VmLib:        7772 kB 进程使用的库映射到虚拟内存空间的大小

VmPTE:         120 kB 进程页表大小
VmSwap:           0 kB

Threads:    5

SigQ:    0/63346

SigPnd:    0000000000000000

ShdPnd:    0000000000000000

SigBlk:    0000000000000000

SigIgn:    0000000001000000

SigCgt:    0000000180000000

CapInh:    0000000000000000

CapPrm:    ffffffffffffffff

CapEff:    ffffffffffffffff

CapBnd:    ffffffffffffffff

Cpus_allowed:    01

Cpus_allowed_list:    0

Mems_allowed:    01

Mems_allowed_list:    0

voluntary_ctxt_switches:    201

nonvoluntary_ctxt_switches:    909

meminfo

下面是查看整机内存使用情况的文件 /proc/meminfo