I check situation in same environment with 2.6.18-194.el5xen on CentOS. I found following: 1) 'unusable' memory exist 2) When oom state occur, no 'rampaging' oom_killer appear, only bloated application die. This behavior differ from describing above: In Debian oom_killer in same situation starts to kill some random processes with number much higher needed to free required memory.