Re: [Qemu-devel] [PATCH 11/15] qom: use mmap for bigger Objects

[Peter Maydell]

On 28 June 2016 at 10:01, Peter Lieven <address@hidden> wrote:
> Signed-off-by: Peter Lieven <address@hidden>
> ---
>  include/qom/object.h |  1 +
>  qom/object.c         | 20 +++++++++++++++++---
>  2 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/include/qom/object.h b/include/qom/object.h
> index 2f8ac47..c612f3a 100644
> --- a/include/qom/object.h
> +++ b/include/qom/object.h
> @@ -400,6 +400,7 @@ struct Object
>      GHashTable *properties;
>      uint32_t ref;
>      Object *parent;
> +    size_t instance_size;
>  };
>
>  /**
> diff --git a/qom/object.c b/qom/object.c
> index 9743ea4..203162b 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -15,6 +15,7 @@
>  #include "qom/object.h"
>  #include "qom/object_interfaces.h"
>  #include "qemu/cutils.h"
> +#include "qemu/mmap-alloc.h"
>  #include "qapi/visitor.h"
>  #include "qapi-visit.h"
>  #include "qapi/string-input-visitor.h"
> @@ -453,6 +454,12 @@ static void object_deinit(Object *obj, TypeImpl *type)
>      }
>  }
>
> +static void object_munmap(void *opaque)
> +{
> +    Object *obj = opaque;
> +    qemu_anon_ram_munmap(obj, obj->instance_size);
> +}
> +
>  static void object_finalize(void *data)
>  {
>      Object *obj = data;
> @@ -467,16 +474,23 @@ static void object_finalize(void *data)
>      }
>  }
>
> +#define OBJECT_MMAP_THRESH 4096
> +
>  Object *object_new_with_type(Type type)
>  {
>      Object *obj;
>
>      g_assert(type != NULL);
>      type_initialize(type);
> -
> -    obj = g_malloc(type->instance_size);
> +    if (type->instance_size < OBJECT_MMAP_THRESH) {
> +        obj = g_malloc(type->instance_size);
> +        obj->free = g_free;
> +    } else {
> +        obj = qemu_anon_ram_mmap(type->instance_size);
> +        obj->free = object_munmap;
> +    }
> +    obj->instance_size = type->instance_size;
>      object_initialize_with_type(obj, type->instance_size, type);
> -    obj->free = g_free;

This one I disagree with. We should trust the platform malloc
implementation (or g_malloc() in this case), or get it fixed
if it is broken somehow.

thanks
-- PMM