Messages in this thread | | | Date | Fri, 2 Dec 2011 09:40:10 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [rfc 2/3] fs, proc: Introduce the Children: line in /proc/<pid>/status |
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On Thu, 1 Dec 2011 13:54:34 +0400 Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> On Wed, Nov 30, 2011 at 10:05:37AM +0400, Cyrill Gorcunov wrote: > > On Wed, Nov 30, 2011 at 02:00:09PM +0900, KAMEZAWA Hiroyuki wrote: > > > 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. > > > > > > > Hi Kame, good point! Yes, it introduces latency on high loaded systems. > > I must admit I tested this patch on a regular system, where not that much > > processes were launched but technically I think more correct would be to > > switch to children file. I'll tune up the patch. Thanks! > > > > > Isn't it better to add /proc/<pid>/children file or dir (as task)? > > > > > > Thanks, > > > -Kame > > > > > What about this one? > --- > fs, proc: Introduce the /proc/<pid>/children entry > > 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 /proc/<pid>/children entry, > since kernel already knows this kind of information but it was not > yet exported. > > Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org> > Cc: Pavel Emelyanov <xemul@parallels.com> > Cc: Serge Hallyn <serge.hallyn@canonical.com> > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Yes, I like /children file. other points seems to be pointed out by other reviewers.
Thanks, -Kame
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