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先积累一点资料吧:
【FreeBSD操作系统设计与实现】:
There are two strategies that can be used for management of pmap memory resources, such as user-directory or page-table memory. The traditional and easiest approach is for the pmap module to manage its own memory. Under this strategy, the pmap module can grab a fixed amount of wired physical memory at system boot time, map that memory into the kernel's address space, and allocate pieces of the memory as needed for its own data structures.
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An alternative approach, used by the PC, is to use the higher-level virtual-memory code recursively to manage some pmap resources. Here, the 4-Kbyte directory table for each user process is mapped into the address space of the kernel as part of setting up the process and remains resident until the process exits. While a process is running, its page-table entries are mapped into a virtually contiguous 4-Mbyte array of page-table entries in the kernel's address space. |
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