1 files changed, 33 insertions, 1 deletions

diff --git a/drivers/xen/xen-selfballoon.c b/drivers/xen/xen-selfballoon.c
index 146c94897016..7d041cb6da26 100644
--- a/drivers/xen/xen-selfballoon.c
+++ b/drivers/xen/xen-selfballoon.c
@@ -105,6 +105,12 @@ static unsigned int selfballoon_interval __read_mostly = 5;
  */
 static unsigned int selfballoon_min_usable_mb;
 
+/*
+ * Amount of RAM in MB to add to the target number of pages.
+ * Can be used to reserve some more room for caches and the like.
+ */
+static unsigned int selfballoon_reserved_mb;
+
 static void selfballoon_process(struct work_struct *work);
 static DECLARE_DELAYED_WORK(selfballoon_worker, selfballoon_process);
 
@@ -217,7 +223,8 @@ static void selfballoon_process(struct work_struct *work)
                 cur_pages = totalram_pages;
                 tgt_pages = cur_pages; /* default is no change */
                 goal_pages = percpu_counter_read_positive(&vm_committed_as) +
-                                totalreserve_pages;
+                                totalreserve_pages +
+                                MB2PAGES(selfballoon_reserved_mb);
 #ifdef CONFIG_FRONTSWAP
                 /* allow space for frontswap pages to be repatriated */
                 if (frontswap_selfshrinking && frontswap_enabled)
@@ -397,6 +404,30 @@ static DEVICE_ATTR(selfballoon_min_usable_mb, S_IRUGO | S_IWUSR,
                    show_selfballoon_min_usable_mb,
                    store_selfballoon_min_usable_mb);
 
+SELFBALLOON_SHOW(selfballoon_reserved_mb, "%d\n",
+                                selfballoon_reserved_mb);
+
+static ssize_t store_selfballoon_reserved_mb(struct device *dev,
+                                             struct device_attribute *attr,
+                                             const char *buf,
+                                             size_t count)
+{
+        unsigned long val;
+        int err;
+
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+        err = strict_strtoul(buf, 10, &val);
+        if (err || val == 0)
+                return -EINVAL;
+        selfballoon_reserved_mb = val;
+        return count;
+}
+
+static DEVICE_ATTR(selfballoon_reserved_mb, S_IRUGO | S_IWUSR,
+                   show_selfballoon_reserved_mb,
+                   store_selfballoon_reserved_mb);
+
 
 #ifdef CONFIG_FRONTSWAP
 SELFBALLOON_SHOW(frontswap_selfshrinking, "%d\n", frontswap_selfshrinking);
@@ -480,6 +511,7 @@ static struct attribute *selfballoon_attrs[] = {
         &dev_attr_selfballoon_downhysteresis.attr,
         &dev_attr_selfballoon_uphysteresis.attr,
         &dev_attr_selfballoon_min_usable_mb.attr,
+        &dev_attr_selfballoon_reserved_mb.attr,
 #ifdef CONFIG_FRONTSWAP
         &dev_attr_frontswap_selfshrinking.attr,
         &dev_attr_frontswap_hysteresis.attr,