[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, 0 insertions, 4 deletions

diff --git a/fs/exec.c b/fs/exec.c
index ec95e796ec22..21222017549d 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -609,8 +609,6 @@ static inline int de_thread(struct signal_struct *oldsig)
 
 		ptrace_unlink(leader);
 		ptrace_unlink(current);
-		unhash_pid(current);
-		unhash_pid(leader);
 		remove_parent(current);
 		remove_parent(leader);
 		/*
@@ -631,8 +629,6 @@ static inline int de_thread(struct signal_struct *oldsig)
 			current->ptrace = ptrace;
 			__ptrace_link(current, parent);
 		}
-		hash_pid(current);
-		hash_pid(leader);
 		
 		list_add_tail(&current->tasks, &init_task.tasks);
 		state = leader->state;