Storage-Class Memory Write Minimization via Trimmed State
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Solution Overview
Problem
Computer systems face challenges in achieving high performance, low cost, and high endurance memory due to the limitations of Dynamic Random-Access Memory (DRAM) and Storage-Class Memory (SCM), where DRAM has low capacity and high cost, while SCM has limited write endurance.
Innovation Solution
Implementing techniques to minimize writes to each page or subpage of the SCM by tracking write operations, allocating unused pages with low write counts to new virtual machines, and marking de-allocated pages as 'trimmed' to reduce write operations, thereby balancing write distribution and extending the memory subsystem's endurance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If de-allocated memory pages are re-used without minimization writes, then memory allocation efficiency is improved, but write endurance of SCM is degraded
Solution Approach 1:
The patent applies preliminary action by proactively identifying and marking memory pages as trimmed before they are fully de-allocated. This allows the system to prepare the pages for future reuse while minimizing write operations, thus resolving the contradiction between allocation efficiency and write endurance.
Solution Approach 2:
The patent changes the state parameter of memory pages by introducing a 'trimmed' status that differs from traditional allocated/de-allocated states. This parameter change enables the system to reuse pages with minimal writes, simultaneously improving allocation efficiency and preserving write endurance.
2Device complexity
If traditional memory management is used without trimming, then implementation simplicity is maintained, but memory subsystem endurance is reduced
Solution Approach 1:
The patent segments the memory management process into distinct phases: allocation, trimming, and de-allocation. By introducing the trimming phase with minimal writes, the system extends memory endurance while maintaining relatively simple implementation through clear separation of concerns.
Solution Approach 2:
The patent introduces an intermediary 'trimmed' state between allocated and de-allocated states. This intermediary state acts as a buffer that allows pages to be prepared for reuse without requiring full de-allocation writes, thus extending endurance while keeping the management mechanism relatively simple.
3Reliability
If memory pages are fully de-allocated before reuse, then data security is improved, but write operations increase reducing SCM lifetime
Solution Approach 1:
The patent applies preliminary action by performing security-related trimming operations before full de-allocation. This allows the system to address security concerns early in the process while minimizing the number of write operations, thereby preserving SCM lifetime.
Solution Approach 2:
The patent applies partial action by performing minimal trim writes rather than full de-allocation writes. This partial action is sufficient to address security concerns for the trimmed portions while avoiding unnecessary writes to the entire page, thus extending SCM lifetime.
Data Source
AI summary
Disclosed herein are techniques for reducing the number of write operations performed to a storage-class memory in a virtualized environment. In one embodiment, when a memory page is de-allocated from a virtual machine, the memory page and/or the subpages of the memory page are marked as “trimmed” in a control table such that any read to the memory page or subpages is denied, and no physical memory initialization is performed to the memory page or subpages. A de-allocated memory page or subpage is only initialized when it is reallocated and is to be written to by the virtual machine to which the memory page is reallocated.