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

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

ebiederm@xmission.com (Eric W. Biederman) writes:

> Holding a reference to a task_struct pins about 10K of low memory even
> after that task has exited.  Which seems to be at 1 or 2 orders of
> mangnitude more memory than any other data structure in the kernel.
> Not holding a reference to a task_struct and you risk problems with
> pid wrap around.
>
> Even worse because we allow session and process group leaders to exit
> there is no task_struct you can hold onto to prevent pid wrap around
> problems for those kinds of structures.
>
> The task_ref is an small intermediate data structure that other
> structures can point, that solves these problems.  A task_ref will
> always point at the first user of a pid value or contain a NULL
> pointer if there are no longer any users of that pid.

I forgot to note that there is a correctness dependence on an my
kill switch_exec_pids patch.  Without that task_refs will
stop being able to track a pid when we pass it on to
a new process in de_thread.

I built this patchset against Linus latest kernel and not -mm so I think
I may have one or two trivial conflicts with Olegs changes as
well.  In particular I have some changes to unhash_process() that Oleg
has removed, but simply removing that hunch should be all the resolution
that is needed.  Hopefully that won't be a problem..

Eric
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