Similar to 9460dee4b2 ("memory: do not touch code dirty bitmap unless
TCG is enabled", 2015-06-05) but for the migration bitmap - we can
skip the MIGRATION bitmap update if migration not enabled.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 include/exec/memory.h   |  2 ++
 include/exec/ram_addr.h | 12 +++++++++++-
 memory.c                |  2 +-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index e6140e8a04..f29300c54d 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -46,6 +46,8 @@
         OBJECT_GET_CLASS(IOMMUMemoryRegionClass, (obj), \
                          TYPE_IOMMU_MEMORY_REGION)
 
+extern bool global_dirty_log;
+
 typedef struct MemoryRegionOps MemoryRegionOps;
 typedef struct MemoryRegionMmio MemoryRegionMmio;
 
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index 993fb760f3..86bc8e1a4a 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -348,8 +348,13 @@ static inline void cpu_physical_memory_set_dirty_lebitmap(unsigned long *bitmap,
             if (bitmap[k]) {
                 unsigned long temp = leul_to_cpu(bitmap[k]);
 
-                atomic_or(&blocks[DIRTY_MEMORY_MIGRATION][idx][offset], temp);
                 atomic_or(&blocks[DIRTY_MEMORY_VGA][idx][offset], temp);
+
+                if (global_dirty_log) {
+                    atomic_or(&blocks[DIRTY_MEMORY_MIGRATION][idx][offset],
+                              temp);
+                }
+
                 if (tcg_enabled()) {
                     atomic_or(&blocks[DIRTY_MEMORY_CODE][idx][offset], temp);
                 }
@@ -366,6 +371,11 @@ static inline void cpu_physical_memory_set_dirty_lebitmap(unsigned long *bitmap,
         xen_hvm_modified_memory(start, pages << TARGET_PAGE_BITS);
     } else {
         uint8_t clients = tcg_enabled() ? DIRTY_CLIENTS_ALL : DIRTY_CLIENTS_NOCODE;
+
+        if (!global_dirty_log) {
+            clients &= ~(1 << DIRTY_MEMORY_MIGRATION);
+        }
+
         /*
          * bitmap-traveling is faster than memory-traveling (for addr...)
          * especially when most of the memory is not dirty.
diff --git a/memory.c b/memory.c
index 0920c105aa..cff0ea8f40 100644
--- a/memory.c
+++ b/memory.c
@@ -38,7 +38,7 @@
 static unsigned memory_region_transaction_depth;
 static bool memory_region_update_pending;
 static bool ioeventfd_update_pending;
-static bool global_dirty_log = false;
+bool global_dirty_log;
 
 static QTAILQ_HEAD(, MemoryListener) memory_listeners
     = QTAILQ_HEAD_INITIALIZER(memory_listeners);
-- 
2.17.1