Hello! (I am sorry for my bad Eanglish)
I think, that in the driver there is an memory leaks.
Use of memory by a X-server grows in due course though I do nothing,
has simply logged-in and do nothing.
Right after start of a server approximately 7 %
For 5 hours -- approximately 50% (%MEM)
pixmaps 17509K (xrestop)
Athlon 64 3000+