[PATCH] dma-buf: make dma_fence structure a bit smaller v2

[Christian König]

Daniel any more comments on this one?

If not I'm going to push it.

Christian.

Am 08.08.19 um 15:22 schrieb Christian König:
> We clear the callback list on kref_put so that by the time we
> release the fence it is unused. No one should be adding to the cb_list
> that they don't themselves hold a reference for.
>
> This small change is actually making the structure 16% smaller.
>
> v2: add the comment to the code as well.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   include/linux/dma-fence.h | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index 05d29dbc7e62..bea1d05cf51e 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -65,8 +65,14 @@ struct dma_fence_cb;
>   struct dma_fence {
>   	struct kref refcount;
>   	const struct dma_fence_ops *ops;
> -	struct rcu_head rcu;
> -	struct list_head cb_list;
> +	/* We clear the callback list on kref_put so that by the time we
> +	 * release the fence it is unused. No one should be adding to the cb_list
> +	 * that they don't themselves hold a reference for.
> +	 */
> +	union {
> +		struct rcu_head rcu;
> +		struct list_head cb_list;
> +	};
>   	spinlock_t *lock;
>   	u64 context;
>   	u64 seqno;