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this article copy from:
http://linux-mm.org/HighMemory
Basically the system uses the following tactics (for highmem):
- Memory above the physical address of 896MB are temporarily mapped into kernel virtual memory whenever the kernel needs to access that memory.
Data which the kernel frequently needs to access is allocated in the lower 896MB of memory (ZONE_NORMAL) and can be immediately accessed by the kernel (see Temporary mapping).
- Data which the kernel only needs to access occasionally, including page cache, process memory and page tables, are preferentially allocated from ZONE_HIGHMEM.
- The system can have additional physical memory zones to deal with devices that can only perform DMA to a limited amount of physical memory, ZONE_DMA and ZONE_DMA32.
Allocations and pageout pressure on the various memory zones need to be balanced (see Memory Balancing).
本文来自ChinaUnix博客,如果查看原文请点:http://blog.chinaunix.net/u/5933/showart_301299.html |
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