Silent Page Migration via PTE Permission Control
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Solution Overview
Problem
Page migration in computing systems can be disruptive to processes, especially during tasks like graphics rendering, as it involves changing virtual-to-physical address translations, which can lead to interruptions and inefficiencies.
Innovation Solution
A method is introduced where a migration pending indication is stored in the page table entry by disabling read and write permissions, allowing read operations while preventing write operations until migration is complete, and generating silent retry requests for write requests, ensuring seamless operation during page migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If page migration is performed during process execution, then memory management flexibility is improved, but process stability and performance deteriorate due to address translation interruptions
Solution Approach 1:
The system sets a migration pending indication in the page table entry before actually migrating the page. This preliminary action prepares the system by marking the page as pending migration, allowing read operations to continue while write operations are deferred. The actual migration is performed later when it is safe to do so, thus maintaining process stability while enabling memory management flexibility.
2Adaptability or versatility
If page migration is performed during process execution, then memory management flexibility is improved, but operation continuity worsens due to address translation changes
Solution Approach 1:
The system sets a migration pending indication in the page table entry before actually migrating the page. This preliminary action prepares the system by marking the page as pending migration, allowing read operations to continue while write operations are deferred. The actual migration is performed later when it is safe to do so, thus maintaining process stability while enabling memory management flexibility.
Solution Approach 2:
The system allows read operations to continue during the migration pending state, ensuring that useful actions (reads) continue uninterrupted. Write operations are deferred until migration is complete, but this deferral is transparent to the process as the system automatically handles the retry. This maintains continuity of useful action while enabling page migration.
3Device complexity
If read and write permissions are disabled in page table entry to indicate migration pending, then migration tracking is simplified, but operation complexity increases due to silent retry requests
Solution Approach 1:
The system uses the existing read and write permission bits in the page table entry for a dual purpose: their traditional access control function and as a migration pending indication. When both bits are cleared, it indicates the page is pending migration. This multi-functional use simplifies migration tracking by reusing existing hardware structures rather than adding new ones, while the memory management unit automatically handles the complexity of silent retry requests.
Data Source
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AI summary
Systems, apparatuses, and methods for migrating memory pages are disclosed herein. In response to detecting that a migration of a first page between memory locations is being initiated, a first page table entry (PTE) corresponding to the first page is located and a migration pending indication is stored in the first PTE. In one embodiment, the migration pending indication is encoded in the first PTE by disabling read and write permissions. If a translation request targeting the first PTE is received by the MMU and the translation request corresponds to a read request, a read operation is allowed to the first page. Otherwise, if the translation request corresponds to a write request, a write operation to the first page is blocked and a silent retry request is generated and conveyed to the requesting client.