关于options MAXMEM？

wuzhihe

技术内幕上面说BSD检测的内存比实际的物理内存少，需要在内核中添加options MAXMEM选项，是不是只有老版本存在这个问题？

langue

====

一般标题有什么 “内幕” “解密” 的书，都不提内幕，也不解密什么。

====

gvim

# MAXMEM specifies the amount of RAM on the machine; if this is not
# specified, FreeBSD will first read the amount of memory from the CMOS
# RAM, so the amount of memory will initially be limited to 64MB or 16MB
# depending on the BIOS.  If the BIOS reports 64MB, a memory probe will
# then attempt to detect the installed amount of RAM.  If this probe
# fails to detect >64MB RAM you will have to use the MAXMEM option.
# The amount is in kilobytes, so for a machine with 128MB of RAM, it would
# be 131072 (128 * 1024).
[src/sys/i386/conf/NOTES]

简单的说，重点在两个if -- If the BIOS ;  If this probe fails
能检测出来就不手动修改，否则就自己修改。
我想《内幕》的意思应该是指：
>>>(if probe fails)BSD检测的内存比实际的物理内存少，那么才需要在内核中添加options MAXMEM选项

另：
......
* Total memory size may be set by the kernel environment variable
* hw.physmem or the compile-time define MAXMEM.
......
*/
static void
getmemsize(int first)
{
......
[src/sys/i386/i386/machdep.c]

[ 本帖最后由 gvim 于 2007-1-17 20:36 编辑 ]