XPDDS18: Memory Overcommitment in XEN - Huang Zhichao, Huawei
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The document discusses memory overcommitment in Xen, highlighting its application in powering virtual machines beyond physical memory limits, which has been used by over 1000 customers with high efficiency over the past year. It details various techniques for implementing memory overcommitment, such as memory ballooning and sharing, along with optimization strategies to improve performance and reduce resource waste. The summary includes key points on use cases, stability, performance, scalability, and compatibility.
XPDDS18: Memory Overcommitment in XEN - Huang Zhichao, Huawei
- 1. HISILICON SEMICONDUCTORHuawei Confidential Page 1 HUAWEI TECHNOLOGIES CO., LTD. Memory Overcommitment in XEN June, 2018 Zhichao Huang <huangzhichao@huawei.com>
- 2. Agenda • Use cases • Issues & Proposals • Summary
- 3. What is memory overcomitment • Allows users to power on virtual machines (VMs) with a total configured memory that exceeds the memory available on the physical machine. Currently, we use it for: – More than 1000 key customers, 100,000 + VMs – More then 150% overcommitment ratio – More than one year without any bugs
- 4. Use cases • Higher consolidation ratio – Traditional business clouding – Old physical machine and same memory size – server virtualization – All VMs with large memory size, to avoid serious waste of resource – scenario under low loads – VDI, Web service, improve resource utilization • Dynamic resource scheduling – high availability – distributed power management – Software/Hardware upgrades - increase the concurrency of live migration
- 5. How to do it • Memory Popluate on Demand – Basic technique – Not useful only by itself – POD reclaim in Hypervisor is too expensive • Memory Ballooning – Requires a driver inside VMs – Must use it carefully • Memory Sharing – Stable and effective – Works well most of the time Memory Ballooning VM1 VM2 Balloon Free Used Used Free Memory Sharing VM1 VM2 VM3 Physical Memory
- 6. How to do it • Memory Swapping – Guaranteed, in an emergency – Disk I/O speed is the key point • Memory Compression – A nice toy • Memory Overcommitment Policy – When, What, How – Memory Qos (Reservation, shares, limit) Memory Swapping Disk VM VM
- 7. Memory Overcommitment scalability • Lots of optimization in upstream – Use unlocked p2m lookups in hvmemul_rep_movs – Defer the invalidation until the p2m lock is released – Use per-cpu lock instead of global shr-lock – …… • Some other optimization from Huawei – Frequent ipi to invalidate ept on related pCPUs – Global calllock -> per-cpu lock – Ticket lock -> mcs lock(scalable lock) – ……
- 8. Evaluation Results With the optimization, the number of lock wait and each wait consuming are both reduced significantly
- 9. With other feature • With migration / Snapshot / Hiberate – Time consumption is reduced to 1/3 or less • With Guest Dump – Time consumption is reduced to 1/2 or less • With Device Passthrough – Full memory reservation automaticly • ……
- 10. Summary • Use cases • Stability • Performance • Scalability • Compatibility