IO scheduler based IO Controller V2

[Rik van Riel]

Ryo Tsuruta wrote:
> Hi Vivek,
> 
>> Ryo, dm-ioband breaks the notion of classes and priority of CFQ because
>> of FIFO dispatch of buffered bios. Apart from that it tries to provide
>> fairness in terms of actual IO done and that would mean a seeky workload
>> will can use disk for much longer to get equivalent IO done and slow down
>> other applications. Implementing IO controller at IO scheduler level gives
>> us tigher control. Will it not meet your requirements? If you got specific
>> concerns with IO scheduler based contol patches, please highlight these and
>> we will see how these can be addressed.
> 
> I'd like to avoid making complicated existing IO schedulers and other
> kernel codes and to give a choice to users whether or not to use it.
> I know that you chose an approach that using compile time options to
> get the same behavior as old system, but device-mapper drivers can be
> added, removed and replaced while system is running.

I do not believe that every use of cgroups will end up with
a separate logical volume for each group.

In fact, if you look at group-per-UID usage, which could be
quite common on shared web servers and shell servers, I would
expect all the groups to share the same filesystem.

I do not believe dm-ioband would be useful in that configuration,
while the IO scheduler based IO controller will just work.

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