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

Eric W. Biederman
2007-04-10T15:23:26Z

Ingo Molnar <mingo@elte.hu> writes:

> * Eric W. Biederman <ebiederm@xmission.com> wrote:
>
>> > on a second thought: the p->children list is needed for the whole
>> > child/parent task tree, which is needed for sys_getppid().
>>
>> Yes, something Oleg said made me realize that.
>>
>> As long as the reparent isn't to complex it isn't required that we
>> have exactly one list .
>>
>> > The question is, does anything require us to reparent to within the
>> > same thread group?
>>
>> I think my head is finally on straight about this question.
>>
>> Currently there is the silly linux specific parent death signal
>> (pdeath_signal). Oleg's memory was a better than mine on this score.
>>
>> However there is no indication that the parent death signal being sent
>> when a thread leader dies is actually correct, or even interesting. It
>> probably should only be sent when getppid changes.
>>
>> So with pdeath_signal fixed that is nothing that requires us to
>> reparent within the same thread group.
>>
>> I'm trying to remember what the story is now. There is a nasty race
>> somewhere with reparenting, a threaded parent setting SIGCHLD to
>> SIGIGN, and non-default signals that results in an zombie that no one
>> can wait for and reap. It requires being reparented twice to trigger.
>>
>> Anyway it is a real mess and if we can remove the stupid multi-headed
>> child lists things would become much simpler and the problem could not
>> occur.
>>
>> Plus the code would become much simpler...
>>
>> utrace appears to have removed the ptrace_children list and the
>> special cases that entailed.
>
> 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?

Eric