[Qemu-devel] [PATCH qemu v3 01/13] memory: Postpone flatview and dispatch tree building till all devices are added

[Alexey Kardashevskiy <aik@ozlabs.ru>]

Most devices use at least one address space and every time a new address
space is added, flat views and dispatch trees are rebuild for all address
spaces. This is not a problem for a relatively small amount of devices but
even 50 virtio-pci devices use more than 8GB of RAM.

What happens that on every flatview/dispatch rebuild, new arrays are
allocated and old ones release but the release is done via RCU so until
an entire machine is build, they are not released.

This wraps devices creation into memory_region_transaction_begin/commit
to massively reduce amount of flat view/dispatch tree (re)allocations.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v2:
* wrapped qemu_run_machine_init_done_notifiers() as well
---
 vl.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/vl.c b/vl.c
index 9e62e92aea..e4f2ece590 100644
--- a/vl.c
+++ b/vl.c
@@ -4741,12 +4741,16 @@ int main(int argc, char **argv, char **envp)
     igd_gfx_passthru();
 
     /* init generic devices */
+    memory_region_transaction_begin();
+
     rom_set_order_override(FW_CFG_ORDER_OVERRIDE_DEVICE);
     if (qemu_opts_foreach(qemu_find_opts("device"),
                           device_init_func, NULL, NULL)) {
         exit(1);
     }
 
+    memory_region_transaction_commit();
+
     cpu_synchronize_all_post_init();
 
     rom_reset_order_override();
@@ -4829,8 +4833,13 @@ int main(int argc, char **argv, char **envp)
     /* TODO: once all bus devices are qdevified, this should be done
      * when bus is created by qdev.c */
     qemu_register_reset(qbus_reset_all_fn, sysbus_get_default());
+
+    memory_region_transaction_begin();
+
     qemu_run_machine_init_done_notifiers();
 
+    memory_region_transaction_commit();
+
     if (rom_check_and_register_reset() != 0) {
         error_report("rom check and register reset failed");
         exit(1);
-- 
2.11.0