Hhm, After compiling the current gentoo kernel with the following options: n22 /usr/src/linux # grep -e "^CONFIG_VMSPLIT" -e "^CONFIG_PAGE_" .config.old CONFIG_VMSPLIT_3G_OPT=y CONFIG_PAGE_OFFSET=0xB0000000 I could not start my UML image, whereas n22 /usr/src/linux # grep -e "^CONFIG_VMSPLIT" -e "^CONFIG_PAGE_" .config CONFIG_VMSPLIT_3G=y CONFIG_PAGE_OFFSET=0xC0000000 works. (setting Severity to minor b/c Im not sure whether this is expected or a bug)
I'm not particularly surprised it doesn't work, that option tends to break a lot of things. However, I'm unable to find anything that claims it actually doesn't work. Are you using usermode-sources for your UML kernel? If not, could you try that?
I tried the following 4 versions for the UML kernel : tfoerste@n22 ~/workspace $ l /usr/local/bin/linux-2.6.1* /usr/local/bin/linux-2.6.15-usermode-r1 /usr/local/bin/linux-2.6.16-usermode /usr/local/bin/linux-2.6.16-gentoo-r6 /usr/local/bin/linux-2.6.16-usermode-r1 Always the same behaviour, my host kernel is currently: Linux n22 2.6.16-gentoo-r7 #6 Mon May 29 14:06:48 CEST 2006 i686 Intel(R) Pentium(R) M processor 1700MHz GNU/Linux I reached this bug while changing my kernel options to better fit my system (1 GB RAM, so I decide to not use the 4GB or the 64 GB config option and in addition I tried a different 3GB/1GB spitting)
I believe that the 3G OPT split doesn't work with UML. UML has a special option to work eith 2G/2G, but not with any of the other optional splits. This should probably be fixed upstream.