[PATCH] libxl: Wait for ballooning if free memory is increasing

[Mike Latimer <mlatimer@suse.com>]

During domain startup, all required memory ballooning must complete
within a maximum window of 33 seconds (3 retries, 11 seconds of delay).
If not, domain creation is aborted with a 'failed to free memory' error.

In order to accommodate large domains or slower hardware (which require
substantially longer to balloon memory) the free memory process should
retry as long as the amount of free memory is increasing on each
iteration of the loop.

---
 tools/libxl/xl_cmdimpl.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 0b02a6c..f87efc0 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -2194,8 +2194,9 @@ static int preserve_domain(uint32_t *r_domid, libxl_event *event,
 
 static int freemem(uint32_t domid, libxl_domain_build_info *b_info)
 {
-    int rc, retries = 3;
-    uint32_t need_memkb, free_memkb;
+    int rc, retries;
+    const int MAX_RETRIES = 3;
+    uint32_t need_memkb, free_memkb, free_memkb_prev = 0;
 
     if (!autoballoon)
         return 0;
@@ -2204,6 +2205,7 @@ static int freemem(uint32_t domid, libxl_domain_build_info *b_info)
     if (rc < 0)
         return rc;
 
+    retries = MAX_RETRIES;
     do {
         rc = libxl_get_free_memory(ctx, &free_memkb);
         if (rc < 0)
@@ -2228,7 +2230,13 @@ static int freemem(uint32_t domid, libxl_domain_build_info *b_info)
         if (rc < 0)
             return rc;
 
-        retries--;
+        /* only decrement retry count if free_memkb is not increasing */
+        if (free_memkb <= free_memkb_prev) {
+            retries--;
+        } else {
+            retries = MAX_RETRIES;
+            free_memkb_prev = free_memkb;
+        }
     } while (retries > 0);
 
     return ERROR_NOMEM;
-- 
1.8.4.5