[PATCH] generic-pidhash-2.5.36-J2, BK-curr

This is the latest version of the generic pidhash patch.  The biggest
change is the removal of separately allocated pid structures: they are
now part of the task structure and the first task that uses a PID will
provide the pid structure.  Task refcounting is used to avoid the
freeing of the task structure before every member of a process group or
session has exited.

This approach has a number of advantages besides the performance gains.
Besides simplifying the whole hashing code significantly, attach_pid()
is now fundamentally atomic and can be called during create_process()
without worrying about task-list side-effects.  It does not have to
re-search the pidhash to find out about raced PID-adding either, and
attach_pid() cannot fail due to OOM.  detach_pid() can do a simple
put_task_struct() instead of the kmem_cache_free().

The only minimal downside is the potential pending task structures after
session leaders or group leaders have exited - but the number of orphan
sessions and process groups is usually very low - and even if it's
higher, this can be regarded as a slow execution of the final
deallocation of the session leader, not some additional burden.

1 files changed, 5 insertions, 0 deletions

diff --git a/kernel/user.c b/kernel/user.c
index 752cda29c965..0704b2aad9c5 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -64,6 +64,11 @@ static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *has
 	return NULL;
 }
 
+struct user_struct *find_user(uid_t uid)
+{
+	return uid_hash_find(uid, uidhashentry(uid));
+}
+
 void free_uid(struct user_struct *up)
 {
 	if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {