Re: [PATCH 3/4] plist: add plist_rotate

[Steven Rostedt <rostedt@goodmis.org>]

On Fri,  2 May 2014 15:02:29 -0400
Dan Streetman <ddstreet@ieee.org> wrote:

> Add plist_rotate(), which moves the specified plist_node after
> all other same-priority plist_nodes in the list.

This is a little confusing? You mean it takes a plist_node from a plist
and simply moves it to the end of the list of all other nodes of the
same priority? Kind of like what a sched_yield() would do with a
SCHED_FIFO task? I wonder if we should call this "plist_yield()" then?

> 
> This is needed by swap, which has a plist of swap_info_structs
> and needs to use each same-priority swap_info_struct equally.

"needs to use each same-priority swap_info_struct equally"

-ENOCOMPUTE

> 
> Also add plist_test_rotate() test function, for use by plist_test()
> to test plist_rotate() function.
> 
> Signed-off-by: Dan Streetman <ddstreet@ieee.org>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> 
> ---
> 
> This patch is new to this patch set, and it's required by the next patch,
> which needs a way to move a plist entry to the end of all following
> same-priority entries.  This is possible to do manually instead of adding
> a new plist function, but having a common plist function instead of code
> specific only to swap seems preferable.
> 
>  include/linux/plist.h |  2 ++
>  lib/plist.c           | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 50 insertions(+)
> 
> diff --git a/include/linux/plist.h b/include/linux/plist.h
> index c815491..06e6925 100644
> --- a/include/linux/plist.h
> +++ b/include/linux/plist.h
> @@ -141,6 +141,8 @@ static inline void plist_node_init(struct plist_node *node, int prio)
>  extern void plist_add(struct plist_node *node, struct plist_head *head);
>  extern void plist_del(struct plist_node *node, struct plist_head *head);
>  
> +extern void plist_rotate(struct plist_node *node, struct plist_head *head);
> +
>  /**
>   * plist_for_each - iterate over the plist
>   * @pos:	the type * to use as a loop counter
> diff --git a/lib/plist.c b/lib/plist.c
> index 1ebc95f..a8b54e5 100644
> --- a/lib/plist.c
> +++ b/lib/plist.c
> @@ -134,6 +134,42 @@ void plist_del(struct plist_node *node, struct plist_head *head)
>  	plist_check_head(head);
>  }
>  
> +/**
> + * plist_rotate - Rotate @node to end of same-prio entries.
> + *
> + * @node:	&struct plist_node pointer - entry to be moved
> + * @head:	&struct plist_head pointer - list head
> + */
> +void plist_rotate(struct plist_node *node, struct plist_head *head)
> +{
> +	struct plist_node *next;
> +	struct list_head *next_node_list = &head->node_list;

Naming convention should be the same as plist_add() and call this
node_next instead of next_node_list.

-- Steve

> +
> +	plist_check_head(head);
> +	BUG_ON(plist_head_empty(head));
> +	BUG_ON(plist_node_empty(node));
> +
> +	if (node == plist_last(head))
> +		return;
> +
> +	next = plist_next(node);
> +
> +	if (node->prio != next->prio)
> +		return;
> +
> +	plist_del(node, head);
> +
> +	plist_for_each_continue(next, head) {
> +		if (node->prio != next->prio) {
> +			next_node_list = &next->node_list;
> +			break;
> +		}
> +	}
> +	list_add_tail(&node->node_list, next_node_list);
> +
> +	plist_check_head(head);
> +}
> +
>  #ifdef CONFIG_DEBUG_PI_LIST
>  #include <linux/sched.h>
>  #include <linux/module.h>
> @@ -170,6 +206,14 @@ static void __init plist_test_check(int nr_expect)
>  	BUG_ON(prio_pos->prio_list.next != &first->prio_list);
>  }
>  
> +static void __init plist_test_rotate(struct plist_node *node)
> +{
> +	plist_rotate(node, &test_head);
> +
> +	if (node != plist_last(&test_head))
> +		BUG_ON(node->prio == plist_next(node)->prio);
> +}
> +
>  static int  __init plist_test(void)
>  {
>  	int nr_expect = 0, i, loop;
> @@ -193,6 +237,10 @@ static int  __init plist_test(void)
>  			nr_expect--;
>  		}
>  		plist_test_check(nr_expect);
> +		if (!plist_node_empty(test_node + i)) {
> +			plist_test_rotate(test_node + i);
> +			plist_test_check(nr_expect);
> +		}
>  	}
>  
>  	for (i = 0; i < ARRAY_SIZE(test_node); i++) {