内核镜像加载地址？

chobit_s

# dmesg|grep -e ".text :" -B 2
      .init : 0xc09da000 - 0xc0a64000   ( 552 kB)
      .data : 0xc0798f98 - 0xc09d9710   (2305 kB)
      .text : 0xc0400000 - 0xc0798f98   (3683 kB)
# dmesg|grep -e "Zone PFN ranges" -A1
Zone PFN ranges:
  DMA      0x00000000 -> 0x00001000

内核镜像加载到物理地址4MB，大小将近6MB
而DMA是前16MB，DMA内存应该是很珍贵的，但是却把内核放入了此段,
这样做，我想不通....

amarant

回复 1# chobit_s


    我想可能有这个原因把，在内核启动之初，还没建立页表，只建立了一个临时内核页表，pg0，pg1两个页全局目录一共8mb，映射的是ram的前8mb，所以只有搬在这前8mb才可以在开启分页机制后继续操作这些内存。

amarant

那又为什么不把临时内核页表建立在16mb开始处呢？

tuibo

什么体系结构，x86 ？ mips,powerpc,arm?

flw2

LZ的这个配置是默认的吗？
我贴一下我的
xcm@u32:/u64/home/xcm/source/linux-2.6$ dmesg|grep -e ".text :" -B 2
[    0.000000]       .init : 0xc168e000 - 0xc1715000   ( 540 kB)
[    0.000000]       .data : 0xc148bd92 - 0xc168db68   (2055 kB)
[    0.000000]       .text : 0xc1000000 - 0xc148bd92   (4655 kB)
xcm@u32:/u64/home/xcm/source/linux-2.6$ uname -an
Linux u32 2.6.37-rc5+ #2 SMP PREEMPT Wed Dec 8 13:34:48 CST 2010 i686 GNU/Linux
xcm@u32:/u64/home/xcm/source/linux-2.6$

最新的内核默认是16MB了


commit ceefccc93932b920a8ec6f35f596db05202a12fe
Author: H. Peter Anvin <hpa@zytor.com>
Date:   Mon May 11 16:12:16 2009 -0700

    x86: default CONFIG_PHYSICAL_START and CONFIG_PHYSICAL_ALIGN to 16 MB
   
    Default CONFIG_PHYSICAL_START and CONFIG_PHYSICAL_ALIGN each to 16 MB,
    so that both non-relocatable and relocatable kernels are loaded at
    16 MB by a non-relocating bootloader.  This is somewhat hacky, but it
    appears to be the only way to do this that does not break some some
    set of existing bootloaders.
   
    We want to avoid the bottom 16 MB because of large page breakup,
    memory holes, and ZONE_DMA.  Embedded systems may need to reduce this,
    or update their bootloaders to be aware of the new min_alignment field.
   
    [ Impact: performance improvement, avoids problems on some systems ]
   
    Signed-off-by: H. Peter Anvin <hpa@zytor.com>

chobit_s

回复 4# tuibo

x86 32 2.6.32.16-141.fc12.i686

chobit_s

回复 5# flw2


    3Q, 这个消息很受用：）

accessory

进来学习下