For every NULL slot in a VMS_ARRAY_OF_POINTER (or every entry of a dynamic array), the saver allocates a 1-element fake VMStateField via g_new0 and frees it again right after the save. For arrays of thousands of entries this is thousands of malloc/free pairs on the hot save path.
Replace the heap-allocated marker with a stack-resident field populated by an init helper. The caller passes a pointer to a local VMStateField, the helper fills it in (still asserting the precondition), and no g_free is needed. Signed-off-by: Bin Guo <[email protected]> --- migration/vmstate.c | 41 ++++++++++++++++------------------------- 1 file changed, 16 insertions(+), 25 deletions(-) diff --git a/migration/vmstate.c b/migration/vmstate.c index 2f13b48a37..9ced78532f 100644 --- a/migration/vmstate.c +++ b/migration/vmstate.c @@ -59,29 +59,23 @@ vmstate_field_exists(const VMStateDescription *vmsd, const VMStateField *field, * array of a VMS_ARRAY_OF_POINTER VMSD field. It's needed because we * can't dereference the NULL pointer. */ -static const VMStateField * -vmsd_create_ptr_marker_field(const VMStateField *field) +static void +vmsd_init_ptr_marker_field(VMStateField *fake, const VMStateField *field) { - VMStateField *fake = g_new0(VMStateField, 1); - /* It can only happen on an array of pointers! */ assert(field->flags & VMS_ARRAY_OF_POINTER); - /* Some of fake's properties should match the original's */ - fake->name = field->name; - fake->version_id = field->version_id; - - /* Do not need "field_exists" check as it always exists */ - fake->field_exists = NULL; - - /* See vmstate_info_ptr_marker - use 1 byte to represent ptr status */ - fake->size = 1; - fake->info = &vmstate_info_ptr_marker; - fake->flags = VMS_SINGLE; - - /* All the rest fields shouldn't matter.. */ - - return (const VMStateField *)fake; + /* See vmstate_info_ptr_marker - 1 byte represents ptr status */ + *fake = (VMStateField) { + .name = field->name, + .version_id = field->version_id, + /* Marker always exists, no field_exists callback needed */ + .field_exists = NULL, + .size = 1, + .info = &vmstate_info_ptr_marker, + .flags = VMS_SINGLE, + /* All other fields stay zero-initialised */ + }; } static int vmstate_n_elems(void *opaque, const VMStateField *field) @@ -680,6 +674,7 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, for (i = 0; i < n_elems; i++) { void *curr_elem = first_elem + size * i; const VMStateField *inner_field; + VMStateField marker_field; /* maximum number of elements to compress in the JSON blob */ int max_elems = vmsd_can_compress(field) ? (n_elems - i) : 1; bool use_marker_field, is_null = false; @@ -693,7 +688,8 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, use_marker_field = use_dynamic_array || is_null; if (use_marker_field) { - inner_field = vmsd_create_ptr_marker_field(field); + vmsd_init_ptr_marker_field(&marker_field, field); + inner_field = &marker_field; } else { inner_field = field; } @@ -730,11 +726,6 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, inner_field, vmdesc_loop, i, max_elems, errp); - /* If we used a fake temp field.. free it now */ - if (use_marker_field) { - g_clear_pointer((gpointer *)&inner_field, g_free); - } - if (!ok) { goto out; } -- 2.50.1 (Apple Git-155)
