Re: [ckrm-tech] [PATCH] BC: resource beancounters (v4) (added user memory)

[Balbir Singh <balbir@in.ibm.com>]

Pavel Emelianov wrote:
> Balbir Singh wrote:
> 
> [snip]
> 
>> This approach has the following disadvantages
>>  1. Lets consider initialization - When we create 'n' groups
>> initially, we need
>>     to spend O(n^2) time to assign guarantees.
> 
> 1. Not guarantees - limits. If you do not need guarantees - assign
>    overcommited limits. Most of OpenVZ users do so and nobody claims.
> 2. If you start n groups at once then limits are calculated in O(n)
>    time, not O(n^2).

Yes.. if you start them at once, but if they are incrementally
added and started it is O(n^2)

> 
>>  2. Every time a limit or a guarantee changes, we need to recalculate
>> guarantees
>>     and ensure that the change will not break any guarantees
> 
> The same.
> 
>>  3. The same thing as stated above, when a resource group is created
>> or deleted
>>
>> This can lead to some instability; a change in one group propagates to
>> all other groups.
> 
> Let me cite a part of your answer on my letter from 11.09.2006:
> "...
>   xemul> I have a node with 1Gb of ram and 10 containers with 100Mb
>   xemul> guarantee each. I want to start one more.
>   xemul> What shall I do not to break guarantees?
> 
>  Don't start the new container or change the guarantees of the
>  existing ones to accommodate this one ... It would be perfectly
>  ok to have a container that does not care about guarantees to
>  set their guarantee to 0 and set their limit to the desired value
> ..."
> 
> The same for the limiting - either do not start new container, or
> recalculate limits to meet new requirements. You may not take care of
> guarantees as weel and create an overcommited configuration.
> 
> And one more thing. We've asked it many times and I ask it again -
> please, show us the other way for providing guarantee rather than
> limiting or reserving.

There are some other options, I am sure Chandra will probably have
more.

1. Reclaim resources from other containers. This can be done well for
    user-pages, if we ensure that each container does not mlock more
    than its guaranteed share of memory.
2. Provide best effort guarantees for non-reclaimable memory
3. oom-kill a container or a task within a resource group that has
    exceeded its guarantee and some other container is unable to meet its
    guarantee

-- 

	Balbir Singh,
	Linux Technology Center,
	IBM Software Labs