> >> Vivek Goyal wrote:
> >>> On Thu, Sep 18, 2008 at 09:04:18PM +0900, Ryo Tsuruta wrote:
> >>>> Hi All,
> >>>>
> >>>> I have got excellent results of dm-ioband, that controls the disk I/O
> >>>> bandwidth even when it accepts delayed write requests.
> >>>>
> >>>> In this time, I ran some benchmarks with a high-end storage. The
> >>>> reason was to avoid a performance bottleneck due to mechanical factors
> >>>> such as seek time.
> >>>>
> >>>> You can see the details of the benchmarks at:
> >>>>
http://people.valinux.co.jp/~ryov/dm-ioband/hps/
> >>>>
> >>> Hi Ryo,
> >>>
> >>> I had a query about dm-ioband patches. IIUC, dm-ioband patches will break
> >>> the notion of process priority in CFQ because now dm-ioband device will
> >>> hold the bio and issue these to lower layers later based on which bio's
> >>> become ready. Hence actual bio submitting context might be different and
> >>> because cfq derives the io_context from current task, it will be broken.
> >>>
> >>> To mitigate that problem, we probably need to implement Fernando's
> >>> suggestion of putting io_context pointer in bio.
> >>>
> >>> Have you already done something to solve this issue?
> >>>
> >>> Secondly, why do we have to create an additional dm-ioband device for
> >>> every device we want to control using rules. This looks little odd
> >>> atleast to me. Can't we keep it in line with rest of the controllers
> >>> where task grouping takes place using cgroup and rules are specified in
> >>> cgroup itself (The way Andrea Righi does for io-throttling patches)?
> >>>
> >>> To avoid creation of stacking another device (dm-ioband) on top of every
> >>> device we want to subject to rules, I was thinking of maintaining an
> >>> rb-tree per request queue. Requests will first go into this rb-tree upon
> >>> __make_request() and then will filter down to elevator associated with the
> >>> queue (if there is one). This will provide us the control of releasing
> >>> bio's to elevaor based on policies (proportional weight, max bandwidth
> >>> etc) and no need of stacking additional block device.
> >>>
> >>> I am working on some experimental proof of concept patches. It will take
> >>> some time though.
> >>>
> >>> I was thinking of following.
> >>>
> >>> - Adopt the Andrea Righi's style of specifying rules for devices and
> >>> group the tasks using cgroups.
> >>>
> >>> - To begin with, adopt dm-ioband's approach of proportional bandwidth
> >>> controller. It makes sense to me limit the bandwidth usage only in
> >>> case of contention. If there is really a need to limit max bandwidth,
> >>> then probably we can do something to implement additional rules or
> >>> implement some policy switcher where user can decide what kind of
> >>> policies need to be implemented.
> >>>
> >>> - Get rid of dm-ioband and instead buffer requests on an rb-tree on every
> >>> request queue which is controlled by some kind of cgroup rules.
> >>>
> >>> It would be good to discuss above approach now whether it makes sense or
> >>> not. I think it is kind of fusion of io-throttling and dm-ioband patches
> >>> with additional idea of doing io-control just above elevator on the request
> >>> queue using an rb-tree.
> >> Thanks Vivek. All sounds reasonable to me and I think this is be the right way
> >> to proceed.
> >>
> >> I'll try to design and implement your rb-tree per request-queue idea into my
> >> io-throttle controller, maybe we can reuse it also for a more generic solution.
> >> Feel free to send me your experimental proof of concept if you want, even if
> >> it's not yet complete, I can review it, test and contribute.
> >
> > Currently I have taken code from bio-cgroup to implement cgroups and to
> > provide functionality to associate a bio to a cgroup. I need this to be
> > able to queue the bio's at right node in the rb-tree and then also to be
> > able to take a decision when is the right time to release few requests.
> >
> > Right now in crude implementation, I am working on making system boot.
> > Once patches are at least in little bit working shape, I will send it to you
> > to have a look.
> >
> > Thanks
> > Vivek
>
> I wonder... wouldn't be simpler to just use the memory controller
> to retrieve this information starting from struct page?
>
> I mean, following this path (in short, obviously using the appropriate
> interfaces for locking and referencing the different objects):
>
> cgrp = page->page_cgroup->mem_cgroup->css.cgroup
>
> Once you get the cgrp it's very easy to use the corresponding controller
> structure.
>
> Actually, this is how I'm doing in cgroup-io-throttle to associate a bio
> to a cgroup. What other functionalities/advantages bio-cgroup provide in
> addition to that?
