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

From: Vivek Goyal
Date: Mon Aug 02 2010 - 16:59:28 EST

On Thu, Jul 08, 2010 at 10:57:13PM -0400, Munehiro Ikeda wrote:
> 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.
> (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.


You will require one more piece and that is support for per cgroup request
descriptors on request queue. With writes, it is so easy to consume those
128 request descriptors.

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