memory: merge adjacent segments of a single memory region

Simple implementations of memory routers, for example the Cirrus VGA memory banks
or the 440FX PAM registers can generate adjacent memory regions which are contiguous.
Detect these and merge them; this saves kvm memory slots and shortens lookup times.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

diff --git a/memory.c b/memory.c
index d858b477391a67a81365876dd2c3d483a9896f5e..121f9e144edda996f338cbeb70427a0c937b5060 100644 (file)
--- a/memory.c
+++ b/memory.c
@@ -122,6 +122,34 @@ static void flatview_destroy(FlatView *view)
     qemu_free(view->ranges);
 }
 
+static bool can_merge(FlatRange *r1, FlatRange *r2)
+{
+    return addrrange_end(r1->addr) == r2->addr.start
+        && r1->mr == r2->mr
+        && r1->offset_in_region + r1->addr.size == r2->offset_in_region
+        && r1->dirty_log_mask == r2->dirty_log_mask;
+}
+
+/* Attempt to simplify a view by merging ajacent ranges */
+static void flatview_simplify(FlatView *view)
+{
+    unsigned i, j;
+
+    i = 0;
+    while (i < view->nr) {
+        j = i + 1;
+        while (j < view->nr
+               && can_merge(&view->ranges[j-1], &view->ranges[j])) {
+            view->ranges[i].addr.size += view->ranges[j].addr.size;
+            ++j;
+        }
+        ++i;
+        memmove(&view->ranges[i], &view->ranges[j],
+                (view->nr - j) * sizeof(view->ranges[j]));
+        view->nr -= j - i;
+    }
+}
+
 /* Render a memory region into the global view.  Ranges in @view obscure
  * ranges in @mr.
  */
@@ -209,6 +237,7 @@ static FlatView generate_memory_topology(MemoryRegion *mr)
     flatview_init(&view);
 
     render_memory_region(&view, mr, 0, addrrange_make(0, UINT64_MAX));
+    flatview_simplify(&view);
 
     return view;
 }