最近升到 xorg 1.5.0，某些操作 (terminal 快速更新) 會使 xserver 佔用非常多 cpu，看來是這個問題
Working on it … right now it looks like:
XShm pixmaps got accidentally reenabled in the course of Adam’s changes
Someone (maybe GTK, having tracked it down yet) is taking advantage
of that by creating a shared pixmap and using it as the source for a composite operation.
That is not handled well in EXA and triggers migration of the destination back to system memory. (*)
(*) One of the many cases where we’d be better off creating temporaries in video memory to avoid migration.