一个存储管理的问题

nqdgj2007

书上说ZONE_DMA被映射到0xc0800000开始之后的16m的地方
但是ZONE_DMA物理地址是0-16m,而1m开始处又是内核镜像的位置
那么ZONE_DMA中大部分岂不是变成内核的镜像了阿 为什么还要映射16m的空间呢
还有ZONE_NORMAL又是怎么映射的

[ 本帖最后由 nqdgj2007 于 2009-9-25 13:06 编辑 ]

accessory

看《UNDERSTANDING LINUX KERNEL> 2ND EDITION. 第二章。

renchujiu

从ULK3抄来的：

The ZONE_DMA zone includes page frames that can be used by old ISA-based devices by means of the DMA. (The section "Direct Memory Access (DMA)" in Chapter 13 gives further details on DMA.)

The ZONE_DMA and ZONE_NORMAL zones include the "normal" page frames that can be directly accessed by the kernel through the linear mapping in the fourth gigabyte of the linear address space (see the section "Kernel Page Tables" in Chapter 2). Conversely, the ZONE_HIGHMEM zone includes page frames that cannot be directly accessed by the kernel through the linear mapping in the fourth gigabyte of linear address space (see the section "Kernel Mappings of High-Memory Page Frames" later in this chapter). The ZONE_HIGHMEM zone is always empty on 64-bit architectures.


ZONE_NORMAL: Contains page frames of memory at and above 16 MB and below 896 MB.

原帖由 nqdgj2007 于 2009-9-25 13:05 发表
书上说ZONE_DMA被映射到0xc0800000开始之后的16m的地方
但是ZONE_DMA物理地址是0-16m,而1m开始处又是内核镜像的位置
那么ZONE_DMA中大部分岂不是变成内核的镜像了阿 为什么还要映射16m的空间呢
还有ZONE_NOR ...