Re: [RFC][PATCH 00/11] blkiocg async support

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* Munihiro Ikeda <m-ikeda@ds.jp.nec.com> [2010-07-08 22:57:13]:

> These RFC patches are trial to add async (cached) write support on blkio
> controller.
> 
> Only test which has been done is to compile, boot, and that write bandwidth
> seems prioritized when pages which were dirtied by two different processes in
> different cgroups are written back to a device simultaneously.  I know this
> is the minimum (or less) test but I posted this as RFC because I would like
> to hear your opinions about the design direction in the early stage.
> 
> Patches are for 2.6.35-rc4.
> 
> This patch series consists of two chunks.
> 
> (1) iotrack (patch 01/11 -- 06/11)
> 
> This is a functionality to track who dirtied a page, in exact which cgroup a
> process which dirtied a page belongs to.  Blkio controller will read the info
> later and prioritize when the page is actually written to a block device.
> This work is originated from Ryo Tsuruta and Hirokazu Takahashi and includes
> Andrea Righi's idea.  It was posted as a part of dm-ioband which was one of
> proposals for IO controller.
>

Does this reuse the memcg infrastructure, if so could you please add a
summary of the changes here.
 
> 
> (2) blkio controller modification (07/11 -- 11/11)
> 
> The main part of blkio controller async write support.
> Currently async queues are device-wide and async write IOs are always treated
> as root group.
> These patches make async queues per a cfq_group per a device to control them.
> Async write is handled by flush kernel thread.  Because queue pointers are
> stored in cfq_io_context, io_context of the thread has to have multiple
> cfq_io_contexts per a device.  So these patches make cfq_io_context per an
> io_context per a cfq_group, which means per an io_context per a cgroup per a
> device.
> 
> 
> This might be a piece of puzzle for complete async write support of blkio
> controller.  One of other pieces in my head is page dirtying ratio control.
> I believe Andrea Righi was working on it...how about the situation?
> 

Greg posted the last set of patches, we are yet to see another
iteration.

> And also, I'm thinking that async write support is required by bandwidth
> capping policy of blkio controller.  Bandwidth capping can be done in upper
> layer than elevator.  However I think it should be also done in elevator layer
> in my opinion.  Elevator buffers and sort requests.  If there is another
> buffering functionality in upper layer, it is doubled buffering and it can be
> harmful for elevator's prediction.
>


-- 
	Three Cheers,
	Balbir