CP-49665: VM anti-affinity support for host evacuation - implemented with Psq #5652
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Add func host_to_vm_count_map to be used, rename RefMap to HostMap Signed-off-by: Gang Ji <gang.ji@citrix.com>
fixup review comments Signed-off-by: Gang Ji <gang.ji@citrix.com>
Signed-off-by: Gang Ji <gang.ji@citrix.com>
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I think this is a lot clearer than the previous PR, now that the state is tracked with PSQ and without the complicated state-update mechanism. Also thank you for adding elaborate comments in the code. I personally would have chosen different names for some of the values, but the comments make things clearer. It's worth considering Colin's comments, but otherwise I'm happy with this now.
| | Some ((host, (_, h_size)), rest_hosts) -> ( | ||
| match vm_size <= h_size with | ||
| | true -> | ||
| Some (host, hosts_psq) |
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The only time hosts_psq is not equal to the pool_state if the "minimum" host from the PSQ does not have enough memory to run the VM. In this case, that host is removed from the PSQ and this smaller PSQ is eventually returned to compute_spread_evenly_plan. The latter then continues with the next VM in the list, which will never get a chance to get planned onto the host removed above.
This relies on the fact that the list of VMs is sorted from small to large, such that any following VM will certainly not fit on hosts that have been removed from the pool_state. So this is an optimisation for performance, not necessary for correctness. Is that right?
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This relies on the fact that the list of VMs is sorted from small to large...
Yes. And the checking is only on the VM size. E.g. in previous PR, it would check the can_boot_on, then the current improvement would not work, as even if the current VM couldn't boot on a host, a bigger VM might do.
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Yes, this is only an optimization: if a host is smaller than the current VM, it doesn't need to be considered for the next VM.
Added some comments to make it clear.
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I personally would have chosen different names for some of the values, but the comments make things clearer.
@robhoes , would you please point those names and a better way for them? I think not only for this time but also will be helpful for later PRs, thanks~
| in | ||
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| let ( let* ) o f = match o with None -> f None | p -> p in | ||
| (let* _no_plan = |
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This is quite confusing, as the syntax looks like the plan is just always thrown away...
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It's failed to plan, and has to continue with the next step.
Otherwise, the plan will be returned directly.
This is the opposite of usual pattern succeeded and then continue.
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Host evacuation plan with anti-affinity support will be carried out in 3 phases: 1. Try to get a "spread evenly" plan for anti-affinity VMs, done if all the rest VMs got planned using binpack, otherwise continue. 2. Try to get a "no breach" plan for anti-affinity VMs, done if all the rest VMs got planned using binpack, otherwise continue. 3. Carry out a binpack plan ignoring VM anti-affinity. Signed-off-by: Gang Ji <gang.ji@citrix.com>
Add "groups" "power_state" for VM, vm set_resident_on host Signed-off-by: Gang Ji <gang.ji@citrix.com>
Signed-off-by: Gang Ji <gang.ji@citrix.com>
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minglumlu
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xapi-project:feature/vm-anti-affinity
Host evacuation plan with anti-affinity support will be carried out in 3 phases:
all the rest VMs got planned using binpack, otherwise continue.
got planned using binpack, otherwise continue.