Origin Host Copy-on-Write for VM Live Migration
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Solution Overview
Problem
The existing virtual machine live migration process is inefficient due to excessive data transmission over networks, particularly when multiple virtual machines are migrated concurrently, as it includes transferring unmodified memory pages and often requires retransmission of pages that have been modified after transfer.
Innovation Solution
The solution involves tracking changes to virtual machine memory pages by write-protecting them and storing a copy before allowing modifications, then comparing the stored copy with the actual page to determine if transmission is necessary, optimizing data transfer by only sending pages that have been modified.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all memory pages are transferred during virtual machine live migration, then the destination host receives complete memory state, but network bandwidth is wasted transferring unmodified pages and retransmission occurs when pages are modified after transfer
Solution Approach 1:
The system performs preliminary actions by tracking memory page modifications before transfer completes. The origin host monitors which pages are modified during migration and only transfers those modified pages to the destination host, avoiding unnecessary transfer of unchanged pages and eliminating retransmission overhead.
Solution Approach 2:
The invention extracts only the necessary modified pages from the complete memory state for transfer. Instead of transferring all memory pages, the system identifies and extracts only those pages that have been modified since the migration started, reducing network bandwidth consumption while maintaining memory state integrity.
2Measurement precision
If memory pages are write-protected to track changes, then modification tracking is enabled, but memory access speed may be affected due to additional validation overhead
Solution Approach 1:
The system applies local quality by making memory pages writable only when needed for modification tracking. Most pages remain read-only and access quickly, while only specific pages undergo write-protection when modifications are detected, minimizing the performance impact across the entire memory space.
Solution Approach 2:
The memory subsystem performs self-service by automatically detecting modifications through write-protection mechanisms and notifying the migration system. This eliminates the need for external monitoring and reduces overhead compared to manual tracking methods.
Data Source
AI summary
Systems and methods for reducing network traffic in virtual machine live migration. An example method may comprise: intercepting, by a first computer system, a write access to a memory page by a virtual machine undergoing live migration from the first computer system to a second computer system; storing a copy of the memory page in a memory before allowing the virtual machine to modify the memory page; identifying data to be transmitted to the second computer system responsive to comparing the memory page and the copy of the memory page; and transmitting the data to the second computer system.