exec: avoid realloc in phys_map_node_reserve

this is the first step in reducing the brk heap fragmentation
created by the map->nodes memory allocation. Since the introduction
of RCU the freeing of the PhysPageMaps is delayed so that sometimes
several hundred are allocated at the same time.

Even worse the memory for map->nodes is allocated and shortly
afterwards reallocated. Since the number of nodes it grows
to in the end is the same for all PhysPageMaps remember this value
and at least avoid the reallocation.

The large number of simultaneous allocations (about 450 x 70kB in
my configuration) has to be addressed later.

Signed-off-by: Peter Lieven <pl@kamp.de>
Message-Id: <1468577030-21097-1-git-send-email-pl@kamp.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/exec.c b/exec.c
index 011babd5844d12d84b6f1b36592afbed5b533d2a..60cf46a5b51cf9b8127d0b1747349be52eddde7d 100644 (file)
--- a/exec.c
+++ b/exec.c
@@ -187,10 +187,12 @@ struct CPUAddressSpace {
 
 static void phys_map_node_reserve(PhysPageMap *map, unsigned nodes)
 {
+    static unsigned alloc_hint = 16;
     if (map->nodes_nb + nodes > map->nodes_nb_alloc) {
-        map->nodes_nb_alloc = MAX(map->nodes_nb_alloc * 2, 16);
+        map->nodes_nb_alloc = MAX(map->nodes_nb_alloc, alloc_hint);
         map->nodes_nb_alloc = MAX(map->nodes_nb_alloc, map->nodes_nb + nodes);
         map->nodes = g_renew(Node, map->nodes, map->nodes_nb_alloc);
+        alloc_hint = map->nodes_nb_alloc;
     }
 }