2 files changed, 81 insertions, 10 deletions

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 7ec933d505d2..25fd1bd949d8 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -55,6 +55,7 @@
 #include <linux/memory_hotplug.h>
 #include <linux/percpu-defs.h>
 #include <linux/slab.h>
+#include <linux/sysctl.h>
 
 #include <asm/page.h>
 #include <asm/pgalloc.h>
@@ -71,6 +72,46 @@
 #include <xen/features.h>
 #include <xen/page.h>
 
+static int xen_hotplug_unpopulated;
+
+#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
+
+static int zero;
+static int one = 1;
+
+static struct ctl_table balloon_table[] = {
+        {
+                .procname       = "hotplug_unpopulated",
+                .data           = &xen_hotplug_unpopulated,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &one,
+        },
+        { }
+};
+
+static struct ctl_table balloon_root[] = {
+        {
+                .procname       = "balloon",
+                .mode           = 0555,
+                .child          = balloon_table,
+        },
+        { }
+};
+
+static struct ctl_table xen_root[] = {
+        {
+                .procname       = "xen",
+                .mode           = 0555,
+                .child          = balloon_root,
+        },
+        { }
+};
+
+#endif
+
 /*
  * balloon_process() state:
  *
@@ -99,6 +140,7 @@ static xen_pfn_t frame_list[PAGE_SIZE / sizeof(unsigned long)];
 
 /* List of ballooned pages, threaded through the mem_map array. */
 static LIST_HEAD(ballooned_pages);
+static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
 
 /* Main work function, always executed in process context. */
 static void balloon_process(struct work_struct *work);
@@ -127,6 +169,7 @@ static void __balloon_append(struct page *page)
                 list_add(&page->lru, &ballooned_pages);
                 balloon_stats.balloon_low++;
         }
+        wake_up(&balloon_wq);
 }
 
 static void balloon_append(struct page *page)
@@ -242,7 +285,8 @@ static enum bp_state reserve_additional_memory(void)
         int nid, rc;
         unsigned long balloon_hotplug;
 
-        credit = balloon_stats.target_pages - balloon_stats.total_pages;
+        credit = balloon_stats.target_pages + balloon_stats.target_unpopulated
+                - balloon_stats.total_pages;
 
         /*
          * Already hotplugged enough pages?  Wait for them to be
@@ -323,7 +367,7 @@ static struct notifier_block xen_memory_nb = {
 static enum bp_state reserve_additional_memory(void)
 {
         balloon_stats.target_pages = balloon_stats.current_pages;
-        return BP_DONE;
+        return BP_ECANCELED;
 }
 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
 
@@ -516,6 +560,28 @@ void balloon_set_new_target(unsigned long target)
 }
 EXPORT_SYMBOL_GPL(balloon_set_new_target);
 
+static int add_ballooned_pages(int nr_pages)
+{
+        enum bp_state st;
+
+        if (xen_hotplug_unpopulated) {
+                st = reserve_additional_memory();
+                if (st != BP_ECANCELED) {
+                        mutex_unlock(&balloon_mutex);
+                        wait_event(balloon_wq,
+                                   !list_empty(&ballooned_pages));
+                        mutex_lock(&balloon_mutex);
+                        return 0;
+                }
+        }
+
+        st = decrease_reservation(nr_pages, GFP_USER);
+        if (st != BP_DONE)
+                return -ENOMEM;
+
+        return 0;
+}
+
 /**
  * alloc_xenballooned_pages - get pages that have been ballooned out
  * @nr_pages: Number of pages to get
@@ -526,27 +592,28 @@ int alloc_xenballooned_pages(int nr_pages, struct page **pages)
 {
         int pgno = 0;
         struct page *page;
+        int ret;
+
         mutex_lock(&balloon_mutex);
+
+        balloon_stats.target_unpopulated += nr_pages;
+
         while (pgno < nr_pages) {
                 page = balloon_retrieve(true);
                 if (page) {
                         pages[pgno++] = page;
                 } else {
-                        enum bp_state st;
-                        st = decrease_reservation(nr_pages - pgno, GFP_USER);
-                        if (st != BP_DONE)
+                        ret = add_ballooned_pages(nr_pages - pgno);
+                        if (ret < 0)
                                 goto out_undo;
                 }
         }
         mutex_unlock(&balloon_mutex);
         return 0;
  out_undo:
-        while (pgno)
-                balloon_append(pages[--pgno]);
-        /* Free the memory back to the kernel soon */
-        schedule_delayed_work(&balloon_worker, 0);
         mutex_unlock(&balloon_mutex);
-        return -ENOMEM;
+        free_xenballooned_pages(pgno, pages);
+        return ret;
 }
 EXPORT_SYMBOL(alloc_xenballooned_pages);
 
@@ -566,6 +633,8 @@ void free_xenballooned_pages(int nr_pages, struct page **pages)
                         balloon_append(pages[i]);
         }
 
+        balloon_stats.target_unpopulated -= nr_pages;
+
         /* The balloon may be too large now. Shrink it if needed. */
         if (current_credit())
                 schedule_delayed_work(&balloon_worker, 0);
@@ -623,6 +692,7 @@ static int __init balloon_init(void)
 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
         set_online_page_callback(&xen_online_page);
         register_memory_notifier(&xen_memory_nb);
+        register_sysctl_table(xen_root);
 #endif
 
         /*
diff --git a/include/xen/balloon.h b/include/xen/balloon.h
index 83efdeb243bf..d1767dfb0d95 100644
--- a/include/xen/balloon.h
+++ b/include/xen/balloon.h
@@ -8,6 +8,7 @@ struct balloon_stats {
         /* We aim for 'current allocation' == 'target allocation'. */
         unsigned long current_pages;
         unsigned long target_pages;
+        unsigned long target_unpopulated;
         /* Number of pages in high- and low-memory balloons. */
         unsigned long balloon_low;
         unsigned long balloon_high;