Re: [RFC][PATCH 1/3] locking/mutex: Rework mutex::owner

[Waiman Long]

On 08/23/2016 08:46 AM, Peter Zijlstra wrote:
>   /*
>    * Simple, straightforward mutexes with strict semantics:
> @@ -48,13 +49,9 @@
>    *   locks and tasks (and only those tasks)
>    */
>   struct mutex {
> -	/* 1: unlocked, 0: locked, negative: locked, possible waiters */
> -	atomic_t		count;
> +	atomic_long_t		owner;
>   	spinlock_t		wait_lock;
>   	struct list_head	wait_list;
> -#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_MUTEX_SPIN_ON_OWNER)
> -	struct task_struct	*owner;
> -#endif
>   #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
>   	struct optimistic_spin_queue osq; /* Spinner MCS lock */
>   #endif

I think you should put the wait_lock and osq next to each other to save 
8 bytes in space on 64-bit machines.

Cheers,
Longman