Err, maybe a patch that actually compiles would be useful ..

Index: libvirt-0.4.6/src/xen_unified.c =================================================================== --- libvirt-0.4.6.orig/src/xen_unified.c +++ libvirt-0.4.6/src/xen_unified.c @@ -799,8 +799,15 @@ xenUnifiedDomainSetMaxMemory (virDomainP GET_PRIVATE(dom->conn); int i; + /* Prefer xend for setting max memory */ + if (priv->opened[XEN_UNIFIED_XEND_OFFSET]) { + if (xenDaemonDomainSetMaxMemory (dom, memory) == 0) + return 0; + } + for (i = 0; i < XEN_UNIFIED_NR_DRIVERS; ++i) - if (priv->opened[i] && + if (i != XEN_UNIFIED_XEND_OFFSET && + priv->opened[i] && drivers[i]->domainSetMaxMemory && drivers[i]->domainSetMaxMemory (dom, memory) == 0) return 0;