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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>
This commit is contained in:
Peter Lieven 2016-07-15 12:03:50 +02:00 committed by Paolo Bonzini
parent d211bd6016
commit 101420b886
1 changed files with 3 additions and 1 deletions
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exec.c
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@ -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;
}
}