plist: Shrink struct plist_head

struct plist_head is used in struct task_struct as well as struct
rtmutex. If we can make it smaller, it will also make these structures
smaller as well.

The field prio_list in struct plist_head is seldom used and we can get
its information from the plist_nodes. Removing this field will decrease
the size of plist_head by half.

Signed-off-by:  Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4D107982.9090700@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 35 insertions, 19 deletions

diff --git a/lib/plist.c b/lib/plist.c
index 1471988d9190..8c614d0e6c35 100644
--- a/lib/plist.c
+++ b/lib/plist.c
@@ -59,7 +59,8 @@ static void plist_check_head(struct plist_head *head)
                 WARN_ON_SMP(!raw_spin_is_locked(head->rawlock));
         if (head->spinlock)
                 WARN_ON_SMP(!spin_is_locked(head->spinlock));
-        plist_check_list(&head->prio_list);
+        if (!plist_head_empty(head))
+                plist_check_list(&plist_first(head)->prio_list);
         plist_check_list(&head->node_list);
 }
 
@@ -75,25 +76,33 @@ static void plist_check_head(struct plist_head *head)
  */
 void plist_add(struct plist_node *node, struct plist_head *head)
 {
-        struct plist_node *iter;
+        struct plist_node *first, *iter, *prev = NULL;
+        struct list_head *node_next = &head->node_list;
 
         plist_check_head(head);
         WARN_ON(!plist_node_empty(node));
+        WARN_ON(!list_empty(&node->prio_list));
 
-        list_for_each_entry(iter, &head->prio_list, plist.prio_list) {
-                if (node->prio < iter->prio)
-                        goto lt_prio;
-                else if (node->prio == iter->prio) {
-                        iter = list_entry(iter->plist.prio_list.next,
-                                        struct plist_node, plist.prio_list);
-                        goto eq_prio;
+        if (plist_head_empty(head))
+                goto ins_node;
+
+        first = iter = plist_first(head);
+
+        do {
+                if (node->prio < iter->prio) {
+                        node_next = &iter->node_list;
+                        break;
                 }
-        }
 
-lt_prio:
-        list_add_tail(&node->plist.prio_list, &iter->plist.prio_list);
-eq_prio:
-        list_add_tail(&node->plist.node_list, &iter->plist.node_list);
+                prev = iter;
+                iter = list_entry(iter->prio_list.next,
+                                struct plist_node, prio_list);
+        } while (iter != first);
+
+        if (!prev || prev->prio != node->prio)
+                list_add_tail(&node->prio_list, &iter->prio_list);
+ins_node:
+        list_add_tail(&node->node_list, node_next);
 
         plist_check_head(head);
 }
@@ -108,14 +117,21 @@ void plist_del(struct plist_node *node, struct plist_head *head)
 {
         plist_check_head(head);
 
-        if (!list_empty(&node->plist.prio_list)) {
-                struct plist_node *next = plist_first(&node->plist);
+        if (!list_empty(&node->prio_list)) {
+                if (node->node_list.next != &head->node_list) {
+                        struct plist_node *next;
+
+                        next = list_entry(node->node_list.next,
+                                        struct plist_node, node_list);
 
-                list_move_tail(&next->plist.prio_list, &node->plist.prio_list);
-                list_del_init(&node->plist.prio_list);
+                        /* add the next plist_node into prio_list */
+                        if (list_empty(&next->prio_list))
+                                list_add(&next->prio_list, &node->prio_list);
+                }
+                list_del_init(&node->prio_list);
         }
 
-        list_del_init(&node->plist.node_list);
+        list_del_init(&node->node_list);
 
         plist_check_head(head);
 }