migration: Don't sync volatile memory after migration completes

Syncing volatile memory provides no benefit, instead it can cause
performance issues in some cases.  Only sync memory that is marked as
non-volatile after migration completes on destination.

Signed-off-by: Ben Chaney <[email protected]>
Fixes: bd108a4 (migration: ram: Switch to ram block writeback)
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Peter Xu <[email protected]>
(cherry picked from commit 983899eab4939dc4dff67fa4d822c5b4df7eae21)
Signed-off-by: Michael Tokarev <[email protected]>

Author: BenjaminChaney

migration/ram.c

@@ -3598,7 +3598,9 @@ static int ram_load_cleanup(void *opaque)
     RAMBlock *rb;
 
     RAMBLOCK_FOREACH_NOT_IGNORED(rb) {
-        qemu_ram_block_writeback(rb);
+        if (memory_region_is_nonvolatile(rb->mr)) {
+            qemu_ram_block_writeback(rb);
+        }
     }
 
     xbzrle_load_cleanup();