wm 没有针对 dpi 的设置，不知道怎么回事，在 ubuntu7.10 下 DisplaySize 的设置无效。
dpi 的设置优先级
How the XFree86 and Xorg servers calculate DPI
The DPI of the X server is determined in the following manner:
1. The -dpi command line option has highest priority.
2. If this is not used, the DisplaySize setting in the X config file is used to derive the DPI, given the screen resolution.
3. If no DisplaySize is given, the monitor size values from DDC are used to derive the DPI, given the screen resolution.
4. If DDC does not specify a size, 75 DPI is used by default.
You can check what DPI your X server is set to by running xdpyinfo | grep resolution in a terminal window.
只能使用最高优先级的 -dpi 参数来设置
startx -- -dpi 90
或者修改 /usr/bin/startx
将 defaultserverargs="" 改成 defaultserverargs="-dpi 90"
