Re: init's children list is long and slows reaping children.

Eric W. Biederman
2007-04-10T16:19:09Z

Ingo Molnar <mingo@elte.hu> writes:

> * Eric W. Biederman <ebiederm@xmission.com> wrote:
>
>> > so ... is anyone pursuing this? This would allow us to make
>> > sys_wait4() faster and more scalable: no tasklist_lock bouncing for
>> > example.
>>
>> which part?
>
> all of it :) Everything you mentioned makes sense quite a bit. The
> thread signal handling of do_wait was added in a pretty arbitrary
> fashion so i doubt there are strong requirements in that area. Apps
> might have grown to get used to it meanwhile though, so we've got to do
> it carefully.

I'm looking at. If only because there is a reasonable chance doing this
will fix the races with a threaded init.

However I just found something nasty. The wait __WNOTHREAD flag.

And my quick search seems to find at least one user space applications
that uses it, and it is widely documented so I suspect there are
others :(

I played with moving the lists into signal_struct, and short of
architecture specific users of task->children all I had to touch
were:

include/linux/init_task.h | 2 +-
include/linux/sched.h | 5 +-
kernel/exit.c | 159 +++++++++++++++++++++------------------------
kernel/fork.c | 2 +-
mm/oom_kill.c | 4 +-

So it should be relatively easy to change this child lists around...

Eric