Re: [PATCH 01/23] tref: Implement task references.

[ebiederm@xmission.com (Eric W. Biederman)]

Oleg Nesterov <oleg@tv-sign.ru> writes:

> I think I have a really good idea.
>
> Forget about task ref for a moment. I thinks we can greatly
> simplify the pids management. We don't PIDTYPE_MAX hash tables,
> we need only one.

I like it.  If we run top we wind of with the same number of dynamic
allocations, with task_refs (because /proc uses them).  The amount of
memory utilized is lower.  Probes for unused sessions and process
groups are a little more expensive but not noticeably so.

Unless we can implement do_each_task_pid/while_each_task_pid in terms
of for_each_task_pid.  I am nervous about making the conversion.

During fork is a very nice time to allocate these as it allows the
rest of the code to assume they are always available.

I think we had something similar several years ago, that's where
the name struct pid came from.  But it used a separate head for each
type of pid, and it used a separate structure for what we now embed
in struct task.

It completely breaks my patch for multiple pid spaces. Oh well it
isn't merged anyway. :)

> And noe we can inplement pid_ref almost for free, just add ->count
> to 'struct pid_head'.
>
> What do you think?

I will take a good hard look at it once I send off my patchs to shore
up task_refs in the -mm tree.

Eric