A question about using "vmstat" to get the memory use info of kernel

[Nan Xiao]

Hi all,

My FreeBSD is installed on VMWare Virtual Machine of my desktop, and the version is as follows:  

# uname -a
FreeBSD FreeBSD 10.3-RELEASE-p5 FreeBSD 10.3-RELEASE-p5 #0: Tue Jul 19 17:52:57 CST 2016     root at FreeBSD:/usr/obj/usr/src/sys/NAN_FIRST_BUILD  amd64

I have installed a "hello" driver, and use "vmstat" command to check its buffer info:  

# vmstat -m | head -n 1 && vmstat -m | grep "hello"
         Type InUse MemUse HighUse Requests  Size(s)
 hello_buffer     1     1K       -        1  256
# vmstat -m | head -n 1 && vmstat -m | grep "hello"
         Type InUse MemUse HighUse Requests  Size(s)
 hello_buffer     1     1K       -        1  256
# vmstat -m | head -n 1 && vmstat -m | grep "hello"
         Type InUse MemUse HighUse Requests  Size(s)
# vmstat -m | head -n 1 && vmstat -m | grep "hello"
         Type InUse MemUse HighUse Requests  Size(s)
 hello_buffer     1     1K       -        1  256

I execute "vmstat -m | head -n 1 && vmstat -m | grep "hello"" command 4 times continuously, but the outputs are different. I am sure the "hello" module
is idle during the time. Why does the command output differently?

Thanks very much in advance!


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Nan Xiao (肖楠)
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