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authorPaolo Bonzini <pbonzini@redhat.com>2013-05-06 11:57:21 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2013-07-04 17:42:49 +0200
commit856d72454f03aea26fd61c728762ef9cd1d71512 (patch)
tree3b53d53b76eb3f819ded7a9ae493795398ac85c1 /memory.c
parenta9a0c06dd750cca982f21089099207874b960656 (diff)
memory: add reference counting to FlatView
With this change, a FlatView can be used even after a concurrent update has replaced it. Because we do not yet have RCU, we use a mutex to protect the small critical sections that read/write the as->current_map pointer. Accesses to the FlatView can be done outside the mutex. If a MemoryRegion will be used after the FlatView is unref-ed (or after a MemoryListener callback is returned), a reference has to be added to that MemoryRegion. memory_region_find already does it for the region that it returns. The same will be done for address_space_translate as soon as the dispatch tree is also converted to RCU-style. Reviewed-by: Anthony Liguori <aliguori@us.ibm.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'memory.c')
-rw-r--r--memory.c79
1 files changed, 69 insertions, 10 deletions
diff --git a/memory.c b/memory.c
index 2774cc878f..35553b52a6 100644
--- a/memory.c
+++ b/memory.c
@@ -29,12 +29,26 @@ static unsigned memory_region_transaction_depth;
static bool memory_region_update_pending;
static bool global_dirty_log = false;
+/* flat_view_mutex is taken around reading as->current_map; the critical
+ * section is extremely short, so I'm using a single mutex for every AS.
+ * We could also RCU for the read-side.
+ *
+ * The BQL is taken around transaction commits, hence both locks are taken
+ * while writing to as->current_map (with the BQL taken outside).
+ */
+static QemuMutex flat_view_mutex;
+
static QTAILQ_HEAD(memory_listeners, MemoryListener) memory_listeners
= QTAILQ_HEAD_INITIALIZER(memory_listeners);
static QTAILQ_HEAD(, AddressSpace) address_spaces
= QTAILQ_HEAD_INITIALIZER(address_spaces);
+static void memory_init(void)
+{
+ qemu_mutex_init(&flat_view_mutex);
+}
+
typedef struct AddrRange AddrRange;
/*
@@ -225,6 +239,7 @@ struct FlatRange {
* order.
*/
struct FlatView {
+ unsigned ref;
FlatRange *ranges;
unsigned nr;
unsigned nr_allocated;
@@ -246,6 +261,7 @@ static bool flatrange_equal(FlatRange *a, FlatRange *b)
static void flatview_init(FlatView *view)
{
+ view->ref = 1;
view->ranges = NULL;
view->nr = 0;
view->nr_allocated = 0;
@@ -279,6 +295,18 @@ static void flatview_destroy(FlatView *view)
g_free(view);
}
+static void flatview_ref(FlatView *view)
+{
+ atomic_inc(&view->ref);
+}
+
+static void flatview_unref(FlatView *view)
+{
+ if (atomic_fetch_dec(&view->ref) == 1) {
+ flatview_destroy(view);
+ }
+}
+
static bool can_merge(FlatRange *r1, FlatRange *r2)
{
return int128_eq(addrrange_end(r1->addr), r2->addr.start)
@@ -578,6 +606,17 @@ static void address_space_add_del_ioeventfds(AddressSpace *as,
}
}
+static FlatView *address_space_get_flatview(AddressSpace *as)
+{
+ FlatView *view;
+
+ qemu_mutex_lock(&flat_view_mutex);
+ view = as->current_map;
+ flatview_ref(view);
+ qemu_mutex_unlock(&flat_view_mutex);
+ return view;
+}
+
static void address_space_update_ioeventfds(AddressSpace *as)
{
FlatView *view;
@@ -587,7 +626,7 @@ static void address_space_update_ioeventfds(AddressSpace *as)
AddrRange tmp;
unsigned i;
- view = as->current_map;
+ view = address_space_get_flatview(as);
FOR_EACH_FLAT_RANGE(fr, view) {
for (i = 0; i < fr->mr->ioeventfd_nb; ++i) {
tmp = addrrange_shift(fr->mr->ioeventfds[i].addr,
@@ -609,6 +648,7 @@ static void address_space_update_ioeventfds(AddressSpace *as)
g_free(as->ioeventfds);
as->ioeventfds = ioeventfds;
as->ioeventfd_nb = ioeventfd_nb;
+ flatview_unref(view);
}
static void address_space_update_topology_pass(AddressSpace *as,
@@ -676,14 +716,25 @@ static void address_space_update_topology_pass(AddressSpace *as,
static void address_space_update_topology(AddressSpace *as)
{
- FlatView *old_view = as->current_map;
+ FlatView *old_view = address_space_get_flatview(as);
FlatView *new_view = generate_memory_topology(as->root);
address_space_update_topology_pass(as, old_view, new_view, false);
address_space_update_topology_pass(as, old_view, new_view, true);
+ qemu_mutex_lock(&flat_view_mutex);
+ flatview_unref(as->current_map);
as->current_map = new_view;
- flatview_destroy(old_view);
+ qemu_mutex_unlock(&flat_view_mutex);
+
+ /* Note that all the old MemoryRegions are still alive up to this
+ * point. This relieves most MemoryListeners from the need to
+ * ref/unref the MemoryRegions they get---unless they use them
+ * outside the iothread mutex, in which case precise reference
+ * counting is necessary.
+ */
+ flatview_unref(old_view);
+
address_space_update_ioeventfds(as);
}
@@ -1148,12 +1199,13 @@ void memory_region_sync_dirty_bitmap(MemoryRegion *mr)
FlatRange *fr;
QTAILQ_FOREACH(as, &address_spaces, address_spaces_link) {
- FlatView *view = as->current_map;
+ FlatView *view = address_space_get_flatview(as);
FOR_EACH_FLAT_RANGE(fr, view) {
if (fr->mr == mr) {
MEMORY_LISTENER_UPDATE_REGION(fr, as, Forward, log_sync);
}
}
+ flatview_unref(view);
}
}
@@ -1205,7 +1257,7 @@ static void memory_region_update_coalesced_range_as(MemoryRegion *mr, AddressSpa
AddrRange tmp;
MemoryRegionSection section;
- view = as->current_map;
+ view = address_space_get_flatview(as);
FOR_EACH_FLAT_RANGE(fr, view) {
if (fr->mr == mr) {
section = (MemoryRegionSection) {
@@ -1231,6 +1283,7 @@ static void memory_region_update_coalesced_range_as(MemoryRegion *mr, AddressSpa
}
}
}
+ flatview_unref(view);
}
static void memory_region_update_coalesced_range(MemoryRegion *mr)
@@ -1532,7 +1585,7 @@ MemoryRegionSection memory_region_find(MemoryRegion *mr,
as = memory_region_to_address_space(root);
range = addrrange_make(int128_make64(addr), int128_make64(size));
- view = as->current_map;
+ view = address_space_get_flatview(as);
fr = flatview_lookup(view, range);
if (!fr) {
return ret;
@@ -1553,6 +1606,7 @@ MemoryRegionSection memory_region_find(MemoryRegion *mr,
ret.readonly = fr->readonly;
memory_region_ref(ret.mr);
+ flatview_unref(view);
return ret;
}
@@ -1561,10 +1615,11 @@ void address_space_sync_dirty_bitmap(AddressSpace *as)
FlatView *view;
FlatRange *fr;
- view = as->current_map;
+ view = address_space_get_flatview(as);
FOR_EACH_FLAT_RANGE(fr, view) {
MEMORY_LISTENER_UPDATE_REGION(fr, as, Forward, log_sync);
}
+ flatview_unref(view);
}
void memory_global_dirty_log_start(void)
@@ -1596,7 +1651,7 @@ static void listener_add_address_space(MemoryListener *listener,
}
}
- view = as->current_map;
+ view = address_space_get_flatview(as);
FOR_EACH_FLAT_RANGE(fr, view) {
MemoryRegionSection section = {
.mr = fr->mr,
@@ -1610,6 +1665,7 @@ static void listener_add_address_space(MemoryListener *listener,
listener->region_add(listener, &section);
}
}
+ flatview_unref(view);
}
void memory_listener_register(MemoryListener *listener, AddressSpace *filter)
@@ -1643,6 +1699,10 @@ void memory_listener_unregister(MemoryListener *listener)
void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
{
+ if (QTAILQ_EMPTY(&address_spaces)) {
+ memory_init();
+ }
+
memory_region_transaction_begin();
as->root = root;
as->current_map = g_new(FlatView, 1);
@@ -1664,9 +1724,8 @@ void address_space_destroy(AddressSpace *as)
memory_region_transaction_commit();
QTAILQ_REMOVE(&address_spaces, as, address_spaces_link);
address_space_destroy_dispatch(as);
- flatview_destroy(as->current_map);
+ flatview_unref(as->current_map);
g_free(as->name);
- g_free(as->current_map);
g_free(as->ioeventfds);
}