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>

1 files changed, 29 insertions, 0 deletions

diff --git a/memory.c b/memory.c
index d858b47..121f9e1 100644
--- 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;
 }