Re: [PATCH 2/1] io-controller: Add a new interface "policy" for IO Controller

[Gui Jianfeng <guijianfeng@cn.fujitsu.com>]

Chad Talbott wrote:
> On Wed, Mar 3, 2010 at 3:19 PM, Nauman Rafique <nauman@google.com> wrote:
>> On Wed, Mar 03, 2010 at 09:33:11AM -0500, Vivek Goyal wrote:
>>> On Wed, Mar 03, 2010 at 02:21:11PM +0800, Gui Jianfeng wrote:
>>>> You can use the following format to assigned specific weight for a given
>>>> device:
>>>> #echo "major:minor weight" > blkio.policy
> 
>>> Can we use a different name for per device weight file name than "blkio.policy".
>>> May be "blkio.weight_device" or "blkio.weight_per_device" etc.
> 
> I agree with Vivek here, and his reasoning below.  This becomes more
> important as more attributes are added.
> 
>>> The reason being that "blkio.policy" name might be more suitable to switch
>>> between differnt kind of BW control policies (proportional, max bandwidth etc),
>>> once we implement some kind of max BW controlling policies also. So it
>>> might be a good idea to not use that file name for specifying per device
>>> weights.
>> Well, thinking more about it, what kind of policy you implement on a block
>> device will not be a per cgroup property. It will not be the case that on
>> a device you are implementing max-bw for one cgroup and proportional
>> weight for other cgroup. It probably will be a per device attribute and
>> if need be should be controlled by /sys/block/<dev> interface.
>>
>> Still, being very clear what a particular cgroup file does makes sense. So
>> that in future for max-bw control, we can bring in more cgroup files like
>> blkio.max_bw or blkio.max_iops etc which can co-exist with blkio.weight_device
>> etc.
> 
> Agreed.  I'd like to add that since we are already thinking about
> expanding the policy with more attributes, perhaps
> blkio_update_group_weight_fn in blkio_policy_ops should be renamed to
> blkio_policy_updated_fn.  Then it could be called if the user changed
> any part of the policy.  Further, instead of storing "weight" in
> blkio_cgroup, we could store a blkio_policy_node there instead.  Then
> the handling of whole-cgroup and per-block-device policy items could
> be more regular.
> 
> Some quick code comments:

Hi Chad,

Thanks for the comments.

> 
> policy_parse_and_set() could be simplified with scanf, like:
> 
> if (sscanf(buf, "%d:%d %d", &major, &minor, &temp) != 3)
>         return -EINVAL;

This can't handle the invalid format like following
echo "8:16 500 500 500 ...." > blkio.policy

> 
> blkcg_get_weight() might better be blkcg_get_policy() and it could
> return a per-disk policy node, or fall back to the cgroup policy if
> none existed for this dev.  This would be across policy attributes,
> rather than just weight.

  For the time being, i still choose blkcg_get_weight(). For there's
  only one attributes here, when more attributs is added, then we might
  change the name.

Thanks
Gui

> 
> Thanks,
> Chad
> 
>