xl: extend autoballoon xl.conf option with an "auto" option

autoballoon=1 is not recommened if dom0_mem was used to reduce the
amount of dom0 memory.  Instead of requiring users to change xl.conf
if they do this, extend the autoballoon option with a new choice:
"auto".

With autoballoon="auto", autoballooning will be disabled if dom0_mem
was used on the Xen command line.

For consistency, accept "on" and "off" as valid autoballoon options (1
and 0 are still accepted).

The default remains "on" for now.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

1 files changed, 14 insertions, 7 deletions

diff --git a/docs/man/xl.conf.pod.5 b/docs/man/xl.conf.pod.5
index 7b9fcac2fa..a4ce3e529d 100644
--- a/docs/man/xl.conf.pod.5
+++ b/docs/man/xl.conf.pod.5
@@ -45,15 +45,22 @@ The semantics of each C<KEY> defines which form of C<VALUE> is required.
 
 =over 4
 
-=item B<autoballoon=BOOLEAN>
+=item B<autoballoon="off"|"on"|"auto">
 
-If disabled then C<xl> will not attempt to reduce the amount of memory
-assigned to domain 0 in order to create free memory when starting a
-new domain. You are strongly recommended to set this to C<0>
-(C<False>) if you use the C<dom0_mem> hypervisor command line to
-reduce the amount of memory given to domain 0 by default.
+If set to "on" then C<xl> will automatically reduce the amount of
+memory assigned to domain 0 in order to free memory for new domains.
 
-Default: C<1>
+If set to "off" then C<xl> will not automatically reduce the amount of
+domain 0 memory.
+
+If set to "auto" then auto-ballooning will be disabled if the
+C<dom0_mem> option was provided on the Xen command line.
+
+You are strongly recommended to set this to C<"off"> (or C<"auto">) if
+you use the C<dom0_mem> hypervisor command line to reduce the amount
+of memory given to domain 0 by default.
+
+Default: C<"on">
 
 =item B<run_hotplug_scripts=BOOLEAN>