[gentoo-user] kswapd0 100% CPU with swapoff and no memory demands on system

[Chris Stankevitz]

Hello,

I have a small system:

- 6GB drive

- ext4 partition mounted readonly

- swap partition that is not listed in fstab and not enabled.  (I will
swapon it every few weeks or so if I need it for a large compile job)

- 2 GB RAM

When the system boots it processing video from a USB camera.  The
program dynamically allocates and releases memory while it runs, but
stores no data in memory or on disk (read-only).  The memory usage
does not grow over time.

When things are going well, top looks like so:

===

Tasks:  68 total,   1 running,  67 sleeping,   0 stopped,   0 zombie
%Cpu0  : 88.3 us, 11.7 sy,  0.0 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu1  : 25.5 us,  2.3 sy,  0.0 ni, 72.1 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu2  :  6.0 us,  0.7 sy,  0.0 ni, 93.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu3  : 25.7 us,  2.3 sy,  0.0 ni, 72.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   1861644 total,   161648 used,  1699996 free,     6948 buffers
KiB Swap:        0 total,        0 used,        0 free,    57728 cached

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 2129 root      20   0 1774440  81712  25388 S 160.0  4.4  25:55.46 obt
  705 root      20   0       0      0      0 S   1.0  0.0   0:07.87 kswapd0
 2049 ueyed     20   0  620472  14092  13652 S   1.0  0.8   0:09.34 ueyeusbd


====


Q1: Why does the kswapd0 process from time to time take up 100% CPU?

Q2: Why does top show "cached swap" eventhough I do not have swap mounted?

Q3: Is there anything I can do to prevent kswapd0 from using CPU on my
system?  e.g. disable SWAP in the kernel config

I suspect the answer to Q1 is:

a) kernel is not configured properly for my hardware
 or
b) there is some bad side effect to my readonly root fs

Thank you,

Chris