Incase you get error while starting Xen-Hvm vps :
There was an error while starting the new VPS
Parsing config from /etc/xen/auto/v1016.cfg WARNING: ignoring "vncviewer" option. Use "-V" option of "xl create" to automatically spawn vncviewer. Invalid parameter `type'. libxl: error: libxl_dom.c:345:libxl__build_pre: Couldn't set max vcpu count libxl: error: libxl_create.c:1259:domcreate_rebuild_done: cannot (re-)build domain: -3 libxl: error: libxl.c:1572:libxl__destroy_domid: non-existant domain 19 libxl: error: libxl.c:1531:domain_destroy_callback: unable to destroy guest with domid 19 libxl: error: libxl.c:1460:domain_destroy_cb: destruction of domain 19 failed
Then you can increase Shadow memory for the vps and check.
The stipulation is that there should be 2KB of memory for every one MB
of RAM assigned to the guest domain, plus a few MB per vcpu ( ~2MB).
So if you have 2 vcpu and 6000Mb Ram then you can keep Shadow memory around 16MB (4Mb+12Mb).