Setting oom_adj so that the ssh process gets killed first

Alkis Georgopoulos <[email protected]> Sun, 12 Dec 2010 23:57:42 +0200
Newsgroups gmane.linux.terminal-server.devel
Message-ID <1292191062.3906.14.camel@alkis> 
Sometimes RAM is exhausted on thin clients, usually due to X pixmaps,
and the kernel chooses a process to kill based on
their /proc/pid/oom_score.
`man proc` explains the two files involved: oom_adj, where the priority
is set, and oom_score, where the score is read.

So if a firefox or an openoffice running on the server use a lot of
pixmaps and exhaust the client RAM, what process should die?
The kernel usually kills X, leaving the user processes still running on
the server and the client in an unstable state.

I think the correct process to be killed would be the
  ssh -Y -t -S $LDM_SOCKET -l $LDM_USERNAME $LDM_SERVER...
line in X95-run-x-session.

To tell the kernel to kill that process instead of X, we can add this to
the ssh call:
  -o 'PermitLocalCommand=yes' -o 'LocalCommand=echo 15 > /proc/$PPID/oom_adj'

I tried that manually and it worked well for me, i.e. no user processes
were left on the server and the client was in a stable state after X was
automatically restarted.
Would anyone mind if I committed something based on that?
(or someone could commit it himself, better for me :))


Here's a small script to generate a page with a lot of images so that
you can reproduce firefox exhausting all the RAM:

echo '<html><body>' > index.htm
i=100
while [ $i -lt 300 ]; do
    echo $i
    echo "<img src='800x$i.jpg'><br>" >> index.htm
    convert -size 800x$i radial-gradient:yellow 800x$i.jpg
    i=$(($i+1))
done
echo '</body></html>' >> index.htm

Run `top` and `xrestop` locally to see the memory usage, and increase
the images number if necessary.

Alkis


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