Fwd: [PATCH] Add load average support to makehistory

Matija Nalis mnalis-ml at voyager.hr
Mon Jun 22 21:53:22 UTC 2009

On Mon, Jun 22, 2009 at 09:24:42AM -0700, Russ Allbery wrote:
> Forwarding for Jonathan Kamens, since I don't know where the message
> went in the moderation queue.
> From: Jonathan Kamens <jik at kamens.brookline.ma.us>
> To: inn-workers at isc.org
> Cc: rra at stanford.edu
> Subject: Re: [PATCH] Add load average support to makehistory
> (I don't subscribe to inn-workers; I was alerted by a subscriber to the
> discussion here of my patch.  Please CC me on any replies.)
> I don't know of any mechanism in Linux for limiting the amount of disk I/O
> that a process or process group is allowed to consume.

On Linux, there exists CFQ I/O scheduler in Linux kernel (which is default
since 2.6.18), which does allow setting I/O priorities using ionice(1)
command (which itself works using ioprio_get(2) and ioprio_set(2) syscalls).

It does for I/O bound tasks somewhat roughly similar as what nice(1) does for
CPU priorities.

In particular, it allows lowering I/O priority of the process (ionice -n7)
or even putting it in the idle I/O class (ionice -c3) which only runs when
no other process is waiting for I/O.

More info can be found at http://en.wikipedia.org/wiki/CFQ

> If there's a better solution, I'd love to hear about it, but I'm pretty sure
> nice isn't it.

However, I still think Jonathans patch is good addition - ionice priorities
are only supported in Linux 2.3.13 and above, and they are not perfect
solution (yet). Also, other OSs than Linux may or may not have such
functionalities (mostly they do not, AFAICT)

Opinions above are GNU-copylefted.

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