[PATCH 3/4] plist: add plist_rotate

[Dan Streetman]

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

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

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;
+
+	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++) {
-- 
1.8.3.1

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