[PATCH 3/3] xfs: Sort delayed write buffers before dispatch

[Christoph Hellwig]

> +/*
> + * Compare function is more complex than it needs to be because
> + * the return value is only 32 bits and we are doing comparisons
> + * on 64 bit values
> + */
> +int
> +xfs_buf_cmp(

Should be marked static.

> +void
> +xfs_buf_delwri_sort(
> +	xfs_buftarg_t	*target,
> +	struct list_head *list)
> +{
> +	list_sort(NULL, list, xfs_buf_cmp);
> +}

Same here.  Not sure I would even bother with the wrapper.  Also the
first argument is entirely unused.

>  STATIC int
>  xfsbufd(
>  	void		*data)
>  {
> +	xfs_buftarg_t   *target = (xfs_buftarg_t *)data;
>  
>  	current->flags |= PF_MEMALLOC;
>  
> @@ -1739,6 +1774,8 @@ xfsbufd(
>  	do {
>  		long	age = xfs_buf_age_centisecs * msecs_to_jiffies(10);
>  		long	tout = age;
> +		int	count = 0;
> +		struct list_head tmp;
>  
>  		if (unlikely(freezing(current))) {
>  			set_bit(XBT_FORCE_SLEEP, &target->bt_flags);
> @@ -1753,11 +1790,10 @@ xfsbufd(
>  		schedule_timeout_interruptible(tout);
>  
>  		xfs_buf_delwri_split(target, &tmp, age);
> +		xfs_buf_delwri_sort(target, &tmp);
>  		while (!list_empty(&tmp)) {
> +			struct xfs_buf *bp;
> +			bp = list_first_entry(&tmp, struct xfs_buf, b_list);
>  			list_del_init(&bp->b_list);
>  			xfs_buf_iostrategy(bp);
>  			count++;
> 
>  
>  	if (wait)
>  		blk_run_address_space(target->bt_mapping);
>  
> +	/* Now wait for IO to complete if required. */
> +	while (!list_empty(&wait_list)) {
> +		bp = list_first_entry(&wait_list, struct xfs_buf, b_list);
>  
>  		list_del_init(&bp->b_list);
>  		xfs_iowait(bp);

As a tiny optimization you might want to move this into the if (wait)
block