Cache coloring

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In computer science, cache coloring (also known as page coloring ) is the process of trying to allocate contiguous free pages from the CPU cache viewpoint, to maximize the total number of cached pages by the processor. Cache coloring is typically used by low-level dynamic memory allocation code in the operating system, when mapping virtual memory to physical memory. A virtual memory subsystem that lacks cache coloration is less deterministic with respect to cache performance, since different page allocations from one program executed to the next can cause substantial differences in program performance.

Video Cache coloring

Detail operasi

The indexed CPU cache is physically designed so that addresses in adjacent physical memory blocks take different positions ("cache lines") in the cache, but this does not happen when it comes to virtual memory; when adjacent memory blocks are virtually but not physically allocated, they potentially take the same position in the cache. Coloring is a technique applied in memory management software, which solves this problem by selecting pages that do not compete with neighboring pages.

Physical memory pages are "colored" so pages with different "colors" have different positions in the CPU cache memory. When allocating sequential pages in virtual memory to processes, the kernel gathers pages with different "colors" and maps them to virtual memory. In this way, consecutive pages in virtual memory do not compete for the same cache line.

Maps Cache coloring

Implementations

This code adds a large amount of complexity to the virtual memory allocation subsystem, but the result is worth the effort. The coloring page makes the virtual memory as deterministic as the physical memory is related to the performance of the cache. The page coloring is used in operating systems such as Solaris, FreeBSD, NetBSD, and Windows NT.

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References

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External links

• "Placement Algorithm Pages for Large Real-Indexed Cache," by R. E. Kessler, Mark D. Hill, University of Wisconsin, 1992.
• "Color Memory," by Jochen Liedtke, IBM T. J. Watson Center, November 1996.
• "??????," by Maray, CSDN Technological Blog, 2008.

Source of the article : Wikipedia