[Xen-devel] [PATCH v2 1/2] xen/balloon: Notify a host about a guest memory size limit

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

Notify a host about a guest memory size limit.

Idea of this patch was discussed with Ian Campbell and Ian Jackson.

Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
---
 drivers/xen/balloon.c |   25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index a56776d..856661f 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -65,6 +65,7 @@
 #include <xen/balloon.h>
 #include <xen/features.h>
 #include <xen/page.h>
+#include <xen/xenbus.h>
 
 /*
  * balloon_process() state:
@@ -586,6 +587,9 @@ static void __init balloon_add_region(unsigned long 
start_pfn,
 static int __init balloon_init(void)
 {
        int i;
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+       int rc;
+#endif
 
        if (!xen_domain())
                return -ENODEV;
@@ -621,6 +625,27 @@ static int __init balloon_init(void)
                        balloon_add_region(PFN_UP(xen_extra_mem[i].start),
                                           PFN_DOWN(xen_extra_mem[i].size));
 
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+       /*
+        * Notify a host about our memory size limit.
+        *
+        * The guest-max value is in KiB, so MAX_DOMAIN_PAGES should
+        * be converted respectively. PAGE_SHIFT converts pages to bytes,
+        * hence PAGE_SHIFT - 10.
+        */
+       rc = xenbus_printf(XBT_NIL, "memory", "guest-max", "%lu",
+                               MAX_DOMAIN_PAGES << (PAGE_SHIFT - 10));
+
+       if (rc < 0)
+               pr_info("xen/balloon: Memory hotplug may not be supported "
+                       "in some environments: %i\n", rc);
+#else
+       xenbus_printf(XBT_NIL, "memory", "guest-max", "%lu",
+                       (balloon_stats.current_pages +
+                        balloon_stats.balloon_low +
+                        balloon_stats.balloon_high) << (PAGE_SHIFT - 10));
+#endif
+
        return 0;
 }
 
-- 
1.7.10.4


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