[PATCH] pids: kill PIDTYPE_TGID

This patch kills PIDTYPE_TGID pid_type thus saving one hash table in
kernel/pid.c and speeding up subthreads create/destroy a bit.  It is also a
preparation for the further tref/pids rework.

This patch adds 'struct list_head thread_group' to 'struct task_struct'
instead.

We don't detach group leader from PIDTYPE_PID namespace until another
thread inherits it's ->pid == ->tgid, so we are safe wrt premature
free_pidmap(->tgid) call.

Currently there are no users of find_task_by_pid_type(PIDTYPE_TGID).
Should the need arise, we can use find_task_by_pid()->group_leader.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-By: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 8 insertions, 4 deletions

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 099e70ecf7c7..5b9082cc600f 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -4,7 +4,6 @@
 enum pid_type
 {
         PIDTYPE_PID,
-        PIDTYPE_TGID,
         PIDTYPE_PGID,
         PIDTYPE_SID,
         PIDTYPE_MAX
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a913fca9e70d..99855f694ebd 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -752,6 +752,7 @@ struct task_struct {
 
         /* PID/PID hash table linkage. */
         struct pid pids[PIDTYPE_MAX];
+        struct list_head thread_group;
 
         struct completion *vfork_done;          /* for vfork() */
         int __user *set_child_tid;              /* CLONE_CHILD_SETTID */
@@ -1192,13 +1193,17 @@ extern void wait_task_inactive(task_t * p);
 #define while_each_thread(g, t) \
         while ((t = next_thread(t)) != g)
 
-extern task_t * FASTCALL(next_thread(const task_t *p));
-
 #define thread_group_leader(p)  (p->pid == p->tgid)
 
+static inline task_t *next_thread(task_t *p)
+{
+        return list_entry(rcu_dereference(p->thread_group.next),
+                                task_t, thread_group);
+}
+
 static inline int thread_group_empty(task_t *p)
 {
-        return list_empty(&p->pids[PIDTYPE_TGID].pid_list);
+        return list_empty(&p->thread_group);
 }
 
 #define delay_group_leader(p) \