Kernel Page Grouping for Physical Memory De-fragmentation
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Solution Overview
Problem
Fragmentation in physical memory, where kernel and user pages become intermixed, leading to performance issues due to the difficulty in relocating kernel pages, which is resource-intensive and can impede system performance, especially in systems that require high availability for mission-critical applications.
Innovation Solution
Creating a kernel page-freelist in addition to user page-freelists, where user pages are designated as kernel pages and added to the kernel page-freelist, allowing for the grouping of kernel pages within large pages, reducing the need for kernel page relocation during coalescing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If kernel pages are relocated during coalescing to free up space, then large pages can be coalesced, but system performance deteriorates due to the resource-intensive nature of kernel page relocation
Solution Approach 1:
The patent applies preliminary action by designating user pages as kernel pages and adding them to the kernel page-freelist before coalescing operations are needed. This pre-positioning of pages eliminates the need for resource-intensive kernel page relocation during coalescing, as the required pages are already in place and marked as available.
2Stability of the object's composition
If kernel pages are grouped together in physical memory, then fragmentation is reduced, but the system cannot adapt to dynamic memory allocation needs
Solution Approach 1:
The patent applies dynamics by maintaining a kernel page-freelist that dynamically tracks and manages kernel pages. The system can adaptively allocate and deallocate kernel pages from this freelist based on runtime memory needs, while still maintaining the grouping benefit. The freelist structure allows the system to respond to dynamic allocation requests without scattering kernel pages throughout memory.
3Productivity
If a separate kernel page-freelist is created to manage kernel pages, then page management efficiency improves, but system complexity increases
Solution Approach 1:
The patent applies universality by designing the kernel page-freelist to serve multiple functions: it tracks available kernel pages for allocation, maintains the grouping of kernel pages to reduce fragmentation, and provides a mechanism for efficient coalescing operations. This multi-functional design consolidates what could be multiple separate management structures into a single unified system.
Data Source
AI summary
An approach for de-fragmenting physical memory generally involves grouping kernel pages together based on large pages. The de-fragmentation procedure is triggered, such as by a kernel page-freelist being empty. The first user page from a user page-freelist is selected, marked as a kernel page (e.g., by setting a P_KERNEL bit), added to the kernel page-freelist, and then the large page in which the selected page is identified. Starting with the first small page within the large page, the small pages are processed by the de-fragmentation procedure, resulting in as many small pages as possible being marked as kernel pages and then added to the kernel page-freelist. Later, when a large page is coalesced, the number of kernel pages that must be relocated within the large page being coalesced is reduced or eliminated as a result of the de-fragmentation of the physical memory.