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[dm-devel] Re: IO scheduler based IO Controller V2



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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