Memory profiling the linux kernel on an embedded device

Question

I have an linux kernel 2.6.30 on an ARM based embedded device and I have to do some kernel memory usage profiling on the device.

I am thinking of monitoring the ps output on various kernel threads and modules while I carry out actions like wifi on/off etc.

Can you suggest me:

Which threads I need to monitor? How to monitor the kernel module memory usage?

Answer 1

There are several ways to monitor memory usage in a Linux system. Some may or may not be available depending on

1. What version you are running
2. How the kernel is configured
3. What user-space tools are included in the root file-system

Since Linux typically is a virtual memory system, some statistics may be misleading and/or inaccurate. It is important to dig and understand what each statstic means.

With all that said, I typically monitor memory usage by running vmstat to get an idea of the total memory usage:

# vmstat -s
       127168  total memory
        44072  used memory
        33296  active memory
         2164  inactive memory
        83096  free memory
            0  buffer memory
        20468  swap cache
            0  total swap
            0  used swap
            0  free swap
       582750 non-nice user cpu ticks
            0 nice user cpu ticks
       160883 system cpu ticks
      7448748 idle cpu ticks
            0 IO-wait cpu ticks
        16066 IRQ cpu ticks
        18249 softirq cpu ticks
            0 stolen cpu ticks
            0 pages paged in
            0 pages paged out
            0 pages swapped in
            0 pages swapped out
     15079537 interrupts
     28629740 CPU context switches
   1344249586 boot time
        25532 forks

"free" Will also give you a bird's eye view of the memory usage. If I see anything unexpected, I will look on suspect processes by examining files in procfs. Good files to look at are

/proc/PID/maps - This lists all the memory currently mapped by the process

/proc/PID/smaps - Provides more details about how much memory is resident/shared/dirty/etc... This file can be verbose, but a Python script could be written to generate more meaningful data