[Patch] Don't sync volatile memory

[Chaney, Ben]

Not all pmem regions are backed by non-volatile memory. Syncing volatile
memory provides no benefit, but can cause performance issues is some
cases. Only sync memory that is marked as non-volatile.

Fixes: bd108a44bc29 (migration: ram: Switch to ram block writeback)

---
migration/ram.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/migration/ram.c b/migration/ram.c
index f25ebd9620..e3ab67acd4 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -3930,7 +3930,9 @@ 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();
--
2.40.1