[Qemu-devel] [PATCH v2 04/23] memory: merge adjacent segments of a single memory region

[Avi Kivity <avi@redhat.com>]

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>
---
 memory.c |   29 +++++++++++++++++++++++++++++
 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;
 }
-- 
1.7.5.3