Re: [PATCH 2/3] i/o bandwidth controller infrastructure

[Andrea Righi <righi.andrea@gmail.com>]

Andrew Morton wrote:
> On Fri, 27 Jun 2008 00:36:46 +0200
> Andrea Righi <righi.andrea@gmail.com> wrote:
> 
>>> Does all this code treat /dev/sda1 as a separate device from /dev/sda2?
>>>  If so, that would be broken.
>> Yes, all the partitions are treated as separate devices with
>> (potentially) different limiting rules, but I don't understand why it
>> would be broken... dev_t has both minor and major numbers, so it would
>> be possible to select single partitions as well.
> 
> Well it's functionally broken, isn't it?  A physical disk has a fixed
> IO bandwidth and when the administrator wants to partition that
> bandwidth amongst control groups he will need to consider the entire
> device when doing so?
> 
> I mean, the whole point of this feature and of control groups as a
> whole is isolation.  But /dev/sda1 and /dev/sda2 are very much _not_
> isolated.  Whereas /dev/sda and /dev/sdb are (to a large degree)
> isolated.

well... yes, sounds reasonable. In this case we could just ignore the
minor number and consider only major number as the key to identify a
specific block device (both for userspace<->kernel interface and when
accounting/throttling i/o requests).

-Andrea