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From "Markus Thoemmes" <markus.thoem...@de.ibm.com>
Subject Re: Proposal: Memory Aware Scheduling
Date Thu, 10 May 2018 11:36:28 GMT
Thanks Dominic!

Yep, that's exactly the thought.

Towards your questions:

# 1. How do loadbalancers keep the state:

They stay as they are. The Semaphores today have the cpu-share based calculated slots and
will have the memory based slots in the future. No change needed there in my opinion.

# 2. How are slots shared among loadbalancers:

Same answer as above: Like today! In your example, each loadbalancer will have 16 slots to
give away (assuming 2 controllers). This has a wrinkle in that the maximum possible memory
size must be proportional to the amount of loadbalancers in the system. For a first step,
this might be fine. In the future we need to implement vertical sharding where the loadbalancers
divide the invoker pool to make bigger memory sizes possible again. Good one!

Another wrinkle here is, that with an increasing amount of loadbalancers fragmentation gets
worse. Again, I think for now this is acceptable in that the recommendation on the amount
of controllers is rather small today.

# 3. Throttling mechanism:

Very good one, I missed that in my initial proposal: Today, we limit the number of concurrent
activations, or differently phrased the number of slots occupied at any point in time. Likewise,
the throttling can change to stay "number of slots occupied at any point in time" and will
effectively limit the amount of memory a user can consume in the system, i.e. if a user has
1000 slots free, she can have 250x 512MB activations running, or 500x 256MB activations (or
any mixture of course).

It's important that we provide a migration path though as this will change the behavior in
production systems. We could make the throttling strategy configurable and decide between
"maximumConcurrentActivations", which ignores the weight of an action and behaves just like
today and "memoryAwareWeights" which is the described new way of throttling.

Cheers,
Markus


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