memory: Share special empty FlatView
This shares an cached empty FlatView among address spaces. The empty
FV is used every time when a root MR renders into a FV without memory
sections which happens when MR or its children are not enabled or
zero-sized. The empty_view is not NULL to keep the rest of memory
API intact; it also has a dispatch tree for the same reason.
On POWER8 with 255 CPUs, 255 virtio-net, 40 PCI bridges guest this halves
the amount of FlatView's in use (557 -> 260) and dispatch tables
(~800000 -> ~370000). In an unrelated experiment with 112 non-virtio
devices on x86 ("-M pc"), only 4 FlatViews are alive, and about ~2000
are created at startup.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <20170921085110.25598-16-aik@ozlabs.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 092aa2fc65
)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
stable-2.10
parent
639701e4f2
commit
496f97293e
18
memory.c
18
memory.c
|
@ -317,6 +317,7 @@ static void flatview_unref(FlatView *view)
|
|||
{
|
||||
if (atomic_fetch_dec(&view->ref) == 1) {
|
||||
trace_flatview_destroy_rcu(view, view->root);
|
||||
assert(view->root);
|
||||
call_rcu(view, flatview_destroy, rcu);
|
||||
}
|
||||
}
|
||||
|
@ -760,16 +761,19 @@ static MemoryRegion *memory_region_get_flatview_root(MemoryRegion *mr)
|
|||
}
|
||||
}
|
||||
}
|
||||
if (found == 0) {
|
||||
return NULL;
|
||||
}
|
||||
if (next) {
|
||||
mr = next;
|
||||
continue;
|
||||
}
|
||||
}
|
||||
|
||||
break;
|
||||
return mr;
|
||||
}
|
||||
|
||||
return mr;
|
||||
return NULL;
|
||||
}
|
||||
|
||||
/* Render a memory topology into a list of disjoint absolute ranges. */
|
||||
|
@ -965,12 +969,22 @@ static void address_space_update_topology_pass(AddressSpace *as,
|
|||
|
||||
static void flatviews_init(void)
|
||||
{
|
||||
static FlatView *empty_view;
|
||||
|
||||
if (flat_views) {
|
||||
return;
|
||||
}
|
||||
|
||||
flat_views = g_hash_table_new_full(g_direct_hash, g_direct_equal, NULL,
|
||||
(GDestroyNotify) flatview_unref);
|
||||
if (!empty_view) {
|
||||
empty_view = generate_memory_topology(NULL);
|
||||
/* We keep it alive forever in the global variable. */
|
||||
flatview_ref(empty_view);
|
||||
} else {
|
||||
g_hash_table_replace(flat_views, NULL, empty_view);
|
||||
flatview_ref(empty_view);
|
||||
}
|
||||
}
|
||||
|
||||
static void flatviews_reset(void)
|
||||
|
|
Loading…
Reference in New Issue