Bug 1461476 - Extend sla architecture to consider hugepages-enabled VMs
Extend sla architecture to consider hugepages-enabled VMs
Status: ON_QA
Product: ovirt-engine
Classification: oVirt
Component: Backend.Core (Show other bugs)
4.2.0
Unspecified Unspecified
high Severity high (vote)
: ovirt-4.2.0
: 4.2.0
Assigned To: Martin Sivák
Artyom
: FutureFeature
Depends On: 1481246
Blocks: 1457239
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Reported: 2017-06-14 10:31 EDT by Martin Polednik
Modified: 2017-09-19 07:33 EDT (History)
11 users (show)

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oVirt Team: SLA
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---
rule-engine: ovirt‑4.2?
michal.skrivanek: blocker?
mavital: testing_plan_complete?
rule-engine: planning_ack?
rule-engine: devel_ack+
rule-engine: testing_ack?


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External Trackers
Tracker ID Priority Status Summary Last Updated
oVirt gerrit 79504 master MERGED common: Fix HugePagesUtils units (KiB vs MiB) and make it static 2017-07-19 04:21 EDT
oVirt gerrit 79505 master MERGED scheduling: Add support for HugePages to scheduler 2017-07-19 11:24 EDT

  None (edit)
Description Martin Polednik 2017-06-14 10:31:47 EDT
The scheduler should be able to schedule VMs that have memory backed by memory - such VMs do not consume regular memory pages we normally consider, but rather hugepages from previously allocated pool.

Specification of hugepages feature:
- hugepage cannot be split: VM with 800 MB ram and hugepage size of 1048576 will consume exactly one hugepage
- only the memory backing of the guest is stored on hugepages; QEMU overhead resides in regular memory
- host reports available hugepages for VM scheduling in it's stats
```
    ...
    "hugepages": {
        "1048576": {
            "resv_hugepages": 0,
            "free_hugepages": 16,
            "nr_overcommit_hugepages": 0,
            "surplus_hugepages": 0,
            "vm.free_hugepages": 16, # <--- the amount of hugepages that we may use for VMs (with hugepage size of 1048576)
            "nr_hugepages": 16,
            "nr_hugepages_mempolicy": 16
        },
        "2048": {
            "resv_hugepages": 0,
            "free_hugepages": 0,
            "nr_overcommit_hugepages": 0,
            "surplus_hugepages": 0,
            "vm.free_hugepages": 0, # <--- the amount of hugepages that we may use for VMs (with hugepage size of 2048)
            "nr_hugepages": 0,
            "nr_hugepages_mempolicy": 0
        }
    },
    "dateTime": "2017-06-14T13:02:53 GMT",
    ...
```
- - scheduler *must* use the highlighted field as certain number of system free hugepages may be reserved for something else (e.g. DPDK)
- host reports available hugepages sizes in capabilities
```
    ...
    "hostedEngineDeployed": false,
    "hugepages": [
        1048576,
        2048
    ],
    "kvmEnabled": "true",
    ...
```
- allocating hugepages reduces available system memory by number of hugepages times hugepages size (even if the hugepages are unused)
- - in other words, each hugepage size can be treated as separate memory pool
- - example: if the host has 64 GiB RAM and 14 1048576 hugepages, it's free memory follows 0 <= free memory <= (64 - 14) GiB
- - the hugepages will be allocated at the boot time
- as far as scheduler is concerned, the hugepages cannot be dynamically (de)allocated
- migration for VMs with hugepages is disabled
- memory hot(unplug) is disabled
- no overcommit
- quota support (maximum number of hugepages consumed by user)
- no special permissions required
- not numa aware at the moment
Comment 1 Yaniv Kaul 2017-06-14 11:45:46 EDT
Do we wish to have different clusters for hosts with static huge pages?
Comment 2 Michal Skrivanek 2017-06-15 07:08:30 EDT
it wouldn't really help much with most of the work needed. once scheduler is aware there is not real need to separate. I mean, sure, it may make sense to do that, but I do not see a reason to enforce it
Comment 5 Michal Skrivanek 2017-06-21 06:21:10 EDT
sorry, it was supposed to be an oVirt bug

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