[Xen-devel] [PATCH] xl: extend autoballoon xl.conf option with an "auto" option

[David Vrabel <david.vrabel@xxxxxxxxxx>]

From: David Vrabel <david.vrabel@xxxxxxxxxx>

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" so it is recommended that packagers provide
an xl.cong with autoballoon="auto".

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 docs/man/xl.conf.pod.5 |   21 ++++++++++++++-------
 tools/examples/xl.conf |    2 +-
 tools/libxl/xl.c       |   31 +++++++++++++++++++++++++++++--
 3 files changed, 44 insertions(+), 10 deletions(-)

diff --git a/docs/man/xl.conf.pod.5 b/docs/man/xl.conf.pod.5
index 82c6b20..959f494 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>
 
diff --git a/tools/examples/xl.conf b/tools/examples/xl.conf
index 28ab796..b3db5db 100644
--- a/tools/examples/xl.conf
+++ b/tools/examples/xl.conf
@@ -2,7 +2,7 @@
 
 # automatically balloon down dom0 when xen doesn't have enough free
 # memory to create a domain
-#autoballoon=1
+#autoballoon="auto"
 
 # full path of the lockfile used by xl during domain creation
 #lockfile="/var/lock/xl"
diff --git a/tools/libxl/xl.c b/tools/libxl/xl.c
index ecbcd3b..bddb7be 100644
--- a/tools/libxl/xl.c
+++ b/tools/libxl/xl.c
@@ -47,6 +47,24 @@ enum output_format default_output_format = 
OUTPUT_FORMAT_JSON;
 
 static xentoollog_level minmsglevel = XTL_PROGRESS;
 
+/* Default autoballoon value based on presence of dom0_mem Xen command
+   line option. */
+static int auto_autoballoon(void)
+{
+    const libxl_version_info *info;
+
+    info = libxl_get_version_info(ctx);
+    if (!info) {
+        fprintf(stderr, "libxl_get_version_info failed.\n");
+        return 1; /* default to autoballooning */
+    }
+
+    if (strstr(info->commandline, "dom0_mem"))
+        return 0;
+
+    return 1;
+}
+
 static void parse_global_config(const char *configfile,
                               const char *configfile_data,
                               int configfile_len)
@@ -68,8 +86,17 @@ static void parse_global_config(const char *configfile,
         exit(1);
     }
 
-    if (!xlu_cfg_get_long (config, "autoballoon", &l, 0))
-        autoballoon = l;
+    if (!xlu_cfg_get_string(config, "autoballoon", &buf, 0)) {
+        printf("opt\n");
+        if (!strcmp(buf, "on") || !strcmp(buf, "1"))
+            autoballoon = 1;
+        else if (!strcmp(buf, "off") || !strcmp(buf, "0"))
+            autoballoon = 0;
+        else if (!strcmp(buf, "auto"))
+            autoballoon = auto_autoballoon();
+        else
+            fprintf(stderr, "invalid autoballoon option");
+    }
 
     if (!xlu_cfg_get_long (config, "run_hotplug_scripts", &l, 0))
         run_hotplug_scripts = l;
-- 
1.7.2.5


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