Virtual Storage Point-in-Time Copy via Page Table Duplication
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Solution Overview
Problem
Computer systems face availability issues due to snapshot image creation, which puts them in a non-dispatchable state, leading to time-outs and impaired application performance during error diagnosis and debugging.
Innovation Solution
A method involving creating a point-in-time copy of virtual page content using a second page data structure with a point-in-time page protection bit, allowing for modification prevention and copying of virtual pages, with the copied pages stored in auxiliary storage, enabling simultaneous read and write access without disrupting system operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a snapshot image of working memory is taken for error diagnosis, then error diagnosis capability is improved, but the computer system enters a non-dispatchable state causing time-outs and application program failures
Solution Approach 1:
The patent creates a copy of the page table data structure to enable snapshot image creation without disrupting system operations. By copying the page table rather than taking a traditional snapshot that halts the system, the invention allows error diagnosis to proceed while the system remains dispatchable and operational.
2Measurement precision
If the system is placed in a non-dispatchable state to take a snapshot image, then accurate error diagnosis is achieved, but application programs cannot run properly and time-outs occur
Solution Approach 1:
The invention copies the page table data structure to create an accurate snapshot image for error diagnosis while the system remains in a dispatchable state. This copying mechanism captures the precise state of virtual storage without inducing the time-outs and application failures that occur with traditional snapshot methods.
3Loss of information
If traditional snapshot imaging is used for debugging, then debugging information is captured, but system operations are disrupted and availability is reduced
Solution Approach 1:
The patent implements a copy of the page table data structure that enables debugging information capture while maintaining system availability. The copying approach allows the system to retain full operational capacity during the snapshot process, unlike traditional methods that require system suspension.
Solution Approach 2:
The copied page table acts as an intermediary that provides debugging information without interfering with normal system operations. This intermediary structure allows error diagnosis and debugging while the original system continues to execute application programs without disruption.
Data Source
AI summary
A method includes making in a real storage, a copy of a first page content stored in a first page data structure by creating a second page content in a second data structure, the second page content pointing to actual data pointed to by the first page content, storing the second page content in the second data structure, marking the first page content in the first page data structure with a page protection bit, wherein the page protection bit prevents a modification of the virtual page, in response to an attempt to modify the virtual page, copying the virtual page in the event the first page content in the first page data structure is marked with the page protection bit, storing the copied virtual page in a second virtual storage, and altering the second page content in the second data structure to point to the stored virtual page.