[Xen-devel] [PATCH v2 2/4] libxl_wait_for_memory_target: wait as long as dom0 is making progress

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Decrement wait_secs only if dom0 is making no progress toward reaching
the balloon target, otherwise loop again for free.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Reviewed-by: Mike Latimer <mlatimer@xxxxxxxx>
Tested-by: Mike Latimer <mlatimer@xxxxxxxx>
---
 tools/libxl/libxl.c      |   29 ++++++++++++++++++++++-------
 tools/libxl/libxl.h      |   14 +++++++++++++-
 tools/libxl/xl_cmdimpl.c |    4 ++--
 3 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 088786e..648a227 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -4959,26 +4959,41 @@ int libxl_wait_for_memory_target(libxl_ctx *ctx, 
uint32_t domid, int wait_secs)
 {
     int rc = 0;
     uint32_t target_memkb = 0;
+    uint64_t current_memkb, prev_memkb;
     libxl_dominfo info;
 
+    rc = libxl_get_memory_target(ctx, domid, &target_memkb);
+    if (rc < 0)
+        return rc;
+
     libxl_dominfo_init(&info);
+    prev_memkb = UINT64_MAX;
 
     do {
-        wait_secs--;
         sleep(1);
 
-        rc = libxl_get_memory_target(ctx, domid, &target_memkb);
-        if (rc < 0)
-            goto out;
-
         libxl_dominfo_dispose(&info);
         libxl_dominfo_init(&info);
         rc = libxl_domain_info(ctx, &info, domid);
         if (rc < 0)
             goto out;
-    } while (wait_secs > 0 && (info.current_memkb + info.outstanding_memkb) > 
target_memkb);
 
-    if ((info.current_memkb + info.outstanding_memkb) <= target_memkb)
+        current_memkb = info.current_memkb + info.outstanding_memkb;
+
+        if (current_memkb > prev_memkb)
+        {
+            rc = ERROR_FAIL;
+            goto out;
+        }
+        else if (current_memkb == prev_memkb)
+            wait_secs--;
+        /* if current_memkb < prev_memkb loop for free as progress has
+         * been made */
+
+        prev_memkb = current_memkb;
+    } while (wait_secs > 0 && current_memkb > target_memkb);
+
+    if (current_memkb <= target_memkb)
         rc = 0;
     else
         rc = ERROR_FAIL;
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index e3d2ae8..3e63e42 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -1043,7 +1043,19 @@ int libxl_domain_need_memory(libxl_ctx *ctx, 
libxl_domain_build_info *b_info,
 int libxl_get_free_memory(libxl_ctx *ctx, uint32_t *memkb);
 /* wait for a given amount of memory to be free in the system */
 int libxl_wait_for_free_memory(libxl_ctx *ctx, uint32_t domid, uint32_t 
memory_kb, int wait_secs);
-/* wait for the memory target of a domain to be reached */
+/* 
+ * Wait for the memory target of a domain to be reached. Does not
+ * decrement wait_secs if the domain is making progress toward reaching
+ * the target. If the domain is not making progress, wait_secs is
+ * decremented. If the timeout expires before the target is reached, the
+ * function returns ERROR_FAIL.
+ *
+ * Older versions of this function (Xen 4.5 and older), decremented
+ * wait_secs even if the domain was making progress, resulting in far
+ * lower overall wait times. To make sure that your calling routine
+ * works with new and old implementations of the function, pass enough
+ * time for the guest to reach its target as an argument.
+ */
 int libxl_wait_for_memory_target(libxl_ctx *ctx, uint32_t domid, int 
wait_secs);
 
 int libxl_vncviewer_exec(libxl_ctx *ctx, uint32_t domid, int autopass);
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index f4c4122..2dc7574 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -2226,8 +2226,8 @@ static int freemem(uint32_t domid, 
libxl_domain_build_info *b_info)
         else if (rc != ERROR_NOMEM)
             return rc;
 
-        /* the memory target has been reached but the free memory is still
-         * not enough: loop over again */
+        /* wait until dom0 reaches its target, as long as we are making
+         * progress */
         rc = libxl_wait_for_memory_target(ctx, 0, 1);
         if (rc < 0)
             return rc;
-- 
1.7.10.4


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