linux-kernel - Re: [RFC][PATCH] per-task I/O throttling

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Message-ID: <478744D7.2070802@users.sourceforge.net>
Date:	Fri, 11 Jan 2008 11:28:39 +0100 (MET)
From:	Andrea Righi <righiandr@...rs.sourceforge.net>
To:	Bill Davidsen <davidsen@....com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [RFC][PATCH] per-task I/O throttling

Bill Davidsen wrote:
> Andrea Righi wrote:
>> Allow to limit the bandwidth of I/O-intensive processes, like backup
>> tools running in background, large files copy, checksums on huge files,
>> etc.
>>
>> This kind of processes can noticeably impact the system responsiveness
>> for some time and playing with tasks' priority is not always an
>> acceptable solution.
>>
>> This patch allows to specify a maximum I/O rate in sectors per second
>> for each single process via /proc/<PID>/io_throttle (default is zero,
>> that specify no limit).
>>
> It would seem to me that this would be vastly more useful in the real 
> world if there were a settable default, so that administrators could 
> avoid having to find and tune individual user processes. And it would 
> seem far less common that the admin would want to set the limit *up* for 
> a given process, and it's likely to be one known to the admin, at least 
> by name.
> 
> Of course if you want to do the effort to make it fully tunable, it 
> could have a default by UID or GID. Usful on machines shared by students 
> or managers.

At the moment I'm simply using it to backup my PC by this wrapper:

$ cat iothrottle
#!/bin/sh
[ $# -lt 2 ] && echo "usage: $0 RATE CMD" && exit 1
rate=$1
shift
$* &
trap "kill -9 $!" SIGINT SIGTERM
[ -e /proc/$!/io_throttle ] && echo $rate >/proc/$!/io_throttle
wait %1
$ ./iothrottle 100 tar ...

But I totally agree with you that setting the limits per-UID/per-GID,
instead of per-task, would be actually more useful.

Maybe a nice approach would be to define the UID/GID upper bounds via
configfs (for example) and allow the users to tune the max I/O rate of
their single tasks according to the defined ranges. In this way it could
be even possible to define I/O shaping policies, i.e. give a bandwidth
of 10MB/s to user A, 20MB/s to user B, 30MB/s to group X, etc.

Anyway, I'm wondering if it's possible (and how) to already do this with
process containers...

-Andrea
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