[Qemu-devel] [PATCH] migration/postcopy: use static PostcopyDiscardState instead of allocating it for each block

[Wei Yang <richardw.yang@linux.intel.com>]

Even we need to do discard for each RAMBlock, we still can leverage the
same memory space to store the information.

By doing so, we avoid memory allocation and deallocation to the system
and also avoid potential failure of memory allocation which breaks the
migration.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
---
 migration/postcopy-ram.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index 9faacacc9e..2e6b076bb7 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -1377,8 +1377,7 @@ void postcopy_fault_thread_notify(MigrationIncomingState *mis)
  *   asking to discard individual ranges.
  *
  * @ms: The current migration state.
- * @offset: the bitmap offset of the named RAMBlock in the migration
- *   bitmap.
+ * @offset: the bitmap offset of the named RAMBlock in the migration bitmap.
  * @name: RAMBlock that discards will operate on.
  *
  * returns: a new PDS.
@@ -1386,13 +1385,14 @@ void postcopy_fault_thread_notify(MigrationIncomingState *mis)
 PostcopyDiscardState *postcopy_discard_send_init(MigrationState *ms,
                                                  const char *name)
 {
-    PostcopyDiscardState *res = g_malloc0(sizeof(PostcopyDiscardState));
+    static PostcopyDiscardState res = {0};
 
-    if (res) {
-        res->ramblock_name = name;
-    }
+    res.ramblock_name = name;
+    res.cur_entry = 0;
+    res.nsentwords = 0;
+    res.nsentcmds = 0;
 
-    return res;
+    return &res;
 }
 
 /**
@@ -1449,8 +1449,6 @@ void postcopy_discard_send_finish(MigrationState *ms, PostcopyDiscardState *pds)
 
     trace_postcopy_discard_send_finish(pds->ramblock_name, pds->nsentwords,
                                        pds->nsentcmds);
-
-    g_free(pds);
 }
 
 /*
-- 
2.17.1