TLB Sampling Register for Hot Page Detection
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Solution Overview
Problem
Current memory tiering techniques incur significant performance overhead and provide suboptimal information for making tiering decisions, as they rely on operations that are not efficient for determining hot and cold pages.
Innovation Solution
A performance-enhanced computing system employs a new on-chip sampling register to periodically sample page residency in the translation lookaside buffer (TLB), allowing for accurate assignment of hot pages to a high-performance memory tier and cold pages to a lower-cost memory tier, bypassing high-overhead operations like access or dirty bits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current memory tiering techniques use access or dirty bits to determine hot and cold pages, then tiering decisions can be made, but significant performance overhead is introduced
Solution Approach 1:
The patent extracts the hotness detection function from the traditional access/dirty bit mechanism and implements it through TLB sampling. By sampling only the TLB residency information rather than tracking all page access bits, the system obtains sufficient hotness detection accuracy while avoiding the performance overhead of comprehensive page table operations.
Solution Approach 2:
The patent uses the TLB as a copy or proxy for tracking page hotness. Instead of directly monitoring page table access bits, the system observes residency patterns in the TLB, which serves as a representative sample of actual memory access behavior. This indirect measurement approach reduces overhead while maintaining detection accuracy.
2Speed
If memory tiering operations are implemented frequently to maintain optimal page placement, then access performance to hot pages improves, but performance degradation increases due to overhead
Solution Approach 1:
The patent implements periodic TLB sampling at configured intervals rather than continuous monitoring. This periodic action allows the system to maintain accurate hotness detection while minimizing the frequency of tiering operations, thereby reducing overhead time while still achieving optimal page access speed when migrations occur.
Solution Approach 2:
The TLB naturally maintains residency information as part of its normal address translation function. The patent leverages this self-service characteristic by sampling existing TLB data without requiring additional tracking infrastructure, thus reducing the overhead of tiering operations while maintaining accurate hotness detection.
3Measurement precision
If comprehensive page tracking is performed to accurately identify hot and cold pages, then tiering decision quality improves, but device complexity increases
Solution Approach 1:
The patent extracts only the essential residency information from the complex page table structure and focuses tracking efforts solely on TLB entries. This extraction approach maintains tiering decision accuracy by capturing the most relevant hotness indicator while avoiding the complexity of comprehensive page table management.
Solution Approach 2:
The TLB serves as an intermediary structure that simplifies hotness detection. By using TLB residency as a proxy for page hotness, the patent avoids the complexity of direct page table monitoring while maintaining sufficient accuracy for tiering decisions. The TLB acts as a mediator between the complex page table and the simple tiering decision logic.
Data Source
AI summary
The disclosed technology provides for an improved memory tiering arrangement. In one aspect, an apparatus includes a sampling register and logic, responsive to sequential read requests, to read page data entries stored in successive locations in a TLB and provide page data from the page data entries as sequential outputs of the sampling register. In another aspect, a method includes generating a page residency list based on scanning, via a sampling register, page data entries stored in successive locations in a TLB, determining, for each page, whether the respective page is a hot page or a cold page based on the page residency list, and assigning hot pages to a first memory tier and cold pages to a second memory tier. Scanning page data entries stored in the TLB can include issuing a sequence of read requests to the sampling register sufficient to read all entries in the TLB.