Is there any way to IO rate-limit an individual process inside a vps? I've got a process that md5's a lot of files and I'd like to slow it down so I don't use up all my io tokens.

Linux xxx 2.4.26-linode31-1um #1 Thu Jul 8 18:24:02 EDT 2004 i686 UML User Mode Linux GNU/Linux

if you call the md5 process from a basic bash script you can include a wait command or you could even grep the iotoken counter too make sure you stay above a current amount.

You could spawn the md5 process, fetch the process ID and as long as it is running, use a simple bash script that monitor /proc/io_status, send SIGSTOP to the PID when the bucket is below a fixed value and send a SIGCONT to the PID when the bucket is back above another.

Take a look at this:

http://www.kotalampi.com/scripts/watchtokens

It is watching your system load & available io tokens and will stop and start services if they go too low/high and restart when systems have returned to normal.

You can modify it for your purposes as follows:

Put your start/stop commands to these files:
$startfile ="/etc/rc.d/start.sh";
$stopfile ="/etc/rc.d/stop.sh";

When to stop services (when load/tokens is at these levels):
$maxload = 3.0;
$l = 0.2; # <20% of max io_tokens

When to restart services (when load/tokens is back at these levels):
$minload = 1.1;
$u = 0.5; # >50% of max io_tokens

Cheers,

Risto

The kill -STOP and CONT would work, but it is going to be pretty bursty. I was thinking more towards something that would keep the usage smooth.

I'm scared looking at that code lol

Maybe this won't be that scary...

if($out =~ /^(io_count=)(\d+)(\s+)(io_rate=)(\d+)(\s+)(io_tokens=)(\d+)(\s+)(token_refill=)(\d+)(\s+)(token_max=)(\d+)$/){
$io_rate = $5;
$io_tokens = $8;
$token_refill = $11;
$token_max = $14;
}
else
{
print STDERR "Invalid /proc/io_status syntax\n";
exit(-1);
}

New version is available in the URL above, too.

Risto

(?:pattern) is your friend. ditto with |=

Also check out this thread:

http://www.linode.com/forums/viewtopic.php?t=1147

In the end of that thread caker alludes to an ionice-type capability being available in the future. Anybody know if that's here yet?