In the book to see,

To understand this sentence?

CodePudding user response:

This is relative to the case of a 32-bit system, for a 32-bit system, a total of only 4 g address space, the kernel can only take up one from 0 xc0000000 XFFFFFFFF 0 1 g space, if all linear addresses to physical memory one-to-one correspondence, the kernel can use the physical memory is limited under the 1 g (because the kernel to addressing the 1 g have taken up in the BIOS, hardware footprint and kernel own code, etc.), there is no physical memory address space under 0 xc0000000 counterpart, all in the virtual address to immediately apply to the kernel for physical memory, when using the
So the Linux memory management is specialized in the design of the part 0 xc0000000 + 896 MB or more reserved for the floating window, when the system need to use high memory, this period will be one of the linear address associated with a piece of high memory, do not need could be released, to supply other process with demand,