Linux kernel developer Matthew Wilcox has revived a proposal to expand the concept of "frozen" pages in the kernel's memory management system, aiming to improve efficiency and pave the way for future enhancements.
At the heart of this initiative is the page reference count - a mechanism that tracks how many users are accessing a given memory page. While reference counting is necessary for many pages, there are cases where maintaining this count creates unnecessary overhead, particularly in the slab allocator system which handles small memory allocations.
The proposed changes would expand the use of "frozen" pages - pages that operate without an active reference count. Currently, frozen pages are only used in the hugetlbfs subsystem, but Wilcox's patches would extend this concept to benefit the slab allocator and potentially other areas.
A key part of the implementation involves pushing reference count initialization deeper into the allocation call stack, enabling certain allocation paths to bypass reference counting entirely. New allocation functions would be introduced specifically for handling frozen pages.
The immediate benefit would be improved performance in the slab allocator by eliminating unnecessary atomic operations during page allocation and freeing. However, the broader goal is more ambitious - this work represents a step toward fundamentally restructuring how the kernel manages memory.
The ultimate vision is to streamline the core page structure (struct page) down to a 64-bit descriptor, with type-specific information stored in separate structures. This could reduce memory overhead across the system, as currently page structures consume approximately 1.5% of system memory.
This development is part of a larger ongoing transformation of the kernel's memory management subsystem. While users may not notice these internal changes, they represent careful architectural improvements that should make the kernel more efficient and maintainable in the long term.
The work demonstrates how kernel developers continue to find ways to optimize even deeply embedded systems while maintaining compatibility - comparable to renovating a building's foundation while it remains in use.