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SubjectRe: [rfc 2/3] fs, proc: Introduce the Children: line in /proc/<pid>/status
On Tue, 29 Nov 2011 23:12:54 +0400
Cyrill Gorcunov <gorcunov@openvz.org> wrote:

> From: Pavel Emelyanov <xemul@parallels.com>
>
> There is no easy way to make a reverse parent->children chain
> from the task status, in turn children->parent provided with "PPid"
> field.
>
> So instead of walking over all pids in system to figure out what
> children the task have -- we add explicit "Children" member to
> /proc/<pid>/status since kernel already knows this kind of information
> but it was not yet exported.
>
> Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
> Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
> Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>

I may be too pessimistic but what amount of overhead will this add to
ps -elf/ top ? Assuming an environment 'ps -elf' is called once per a sec,
if there are 2000 processes, task_list lock is taken 2000 times by this patch.

Isn't it better to add /proc/<pid>/children file or dir (as task)?

Thanks,
-Kame



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