Compound Page Table Hybrid Paging Virtual Memory
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Solution Overview
Problem
Current computer systems face inefficiencies in memory address translation, particularly in virtualized environments, where nested-paging scales nonlinearly and shadow-paging requires resource-intensive updates, leading to increased memory accesses and processor usage.
Innovation Solution
A compound page table system that dynamically selects between shadow-paging and nested-paging based on memory address stability, allowing for granular control over translation modes without separate data structures, reducing memory references and optimizing address translation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If shadow-paging is used to translate guest virtual addresses directly to host physical addresses, then the number of memory accesses is reduced, but processor resources are intensively consumed for updates
Solution Approach 1:
The patent implements a dynamic hybrid page table system that automatically adjusts between shadow-paging and nested-paging modes based on runtime conditions. The system monitors memory access patterns and translation frequency, switching to shadow-paging mode when direct translation benefits outweigh update costs, and to nested-paging mode when update overhead becomes prohibitive. This dynamic adaptation resolves the contradiction by optimizing the balance between translation speed and processor resource consumption according to actual system state.
Solution Approach 2:
The patent changes the operational parameters of the page table system by introducing a hybrid mode that combines shadow-paging and nested-paging characteristics. It adjusts the translation mechanism parameters based on memory address stability and access patterns, using shadow-paging entries for stable translations and nested-paging entries for dynamic ones. This parameter adjustment allows the system to achieve fast translation where possible while conserving processor resources where updates would be costly.
2Quantity of substance
If nested-paging is used to translate guest virtual addresses through guest physical addresses to host physical addresses, then memory resources are conserved, but the number of memory accesses increases
Solution Approach 1:
The patent segments the page table translation process into two distinct pathways: shadow-paging entries for direct guest virtual to host physical address translation, and nested-paging entries for traditional two-stage translation. This segmentation allows the system to choose the appropriate path based on memory address stability and access patterns, reducing the number of memory accesses for stable translations while maintaining memory resource efficiency for dynamic translations.
Solution Approach 2:
The patent introduces a hybrid page table structure that acts as an intermediary between the guest virtual address space and host physical address space. This hybrid structure contains both shadow-paging entries (providing direct translation) and nested-paging entries (providing two-stage translation), allowing the system to mediate translation requests based on the specific characteristics of each memory access, thereby optimizing both memory resource usage and translation speed.
3Measurement precision
If a single page table entry is used for each virtual/physical address translation pair, then translation accuracy is maintained, but memory resources are excessively consumed
Solution Approach 1:
The patent merges shadow-paging and nested-paging into a unified hybrid page table structure. This combined structure maintains translation accuracy by ensuring that both shadow-paging entries and nested-paging entries provide correct address translations, while reducing memory resource consumption by using shadow-paging entries for stable translations (requiring fewer entries) and nested-paging entries only when necessary. The hybrid structure consolidates the benefits of both approaches while eliminating their individual drawbacks.
Data Source
AI summary
The translation of virtual guest addresses to host physical addresses in a virtualized computer system provides a compound page table that may simultaneously support nested-paging and shadow-paging for different memory regions. Memory regions with stable address mapping, for example, holding program code, may be treated using shadow-paging while memory regions with dynamic address mapping, for example, variable storage, may be treated using nested-paging thereby obtaining the benefits of both techniques.