On Mon, May 5, 2014 at 10:18 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> On Fri, 2 May 2014 15:02:29 -0400
> Dan Streetman <ddstreet@xxxxxxxx> 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?
yes, exactly
> Kind of like what a sched_yield() would do with a
> SCHED_FIFO task? I wonder if we should call this "plist_yield()" then?
I suppose it is similar, yes...I'll rename it in a v2 patch.
>
>>
>> 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
heh, yeah that needs a bit more explaining doesn't it :-)
by "equally", I mean as swap writes pages out to its swap devices, it
must write to any same-priority devices on a round-robin basis.
I'll update the comment in the v2 patch to try to explain clearer.
>
>>
>> Also add plist_test_rotate() test function, for use by plist_test()
>> to test plist_rotate() function.
>>
>> Signed-off-by: Dan Streetman <ddstreet@xxxxxxxx>
>> Cc: Mel Gorman <mgorman@xxxxxxx>
>> Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
>> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>>
>> ---
>>
>> 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.
ok will do.
>
> -- 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++) {
>
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