Messages in this thread Patch in this message | | | Date | Thu, 1 Dec 2011 13:54:34 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [rfc 2/3] fs, proc: Introduce the Children: line in /proc/<pid>/status |
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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> --- fs/proc/array.c | 14 ++++++++++++++ fs/proc/base.c | 1 + fs/proc/internal.h | 3 +++ 3 files changed, 18 insertions(+)
Index: linux-2.6.git/fs/proc/array.c =================================================================== --- linux-2.6.git.orig/fs/proc/array.c +++ linux-2.6.git/fs/proc/array.c @@ -547,3 +547,17 @@ int proc_pid_statm(struct seq_file *m, s return 0; } + +int proc_pid_children(struct seq_file *m, struct pid_namespace *ns, + struct pid *pid, struct task_struct *task) +{ + struct task_struct *c; + + read_lock(&tasklist_lock); + list_for_each_entry(c, &task->children, sibling) + seq_printf(m, " %d", pid_nr_ns(task_pid(c), ns)); + read_unlock(&tasklist_lock); + seq_putc(m, '\n'); + + return 0; +} Index: linux-2.6.git/fs/proc/base.c =================================================================== --- linux-2.6.git.orig/fs/proc/base.c +++ linux-2.6.git/fs/proc/base.c @@ -3204,6 +3204,7 @@ static const struct pid_entry tgid_base_ INF("cmdline", S_IRUGO, proc_pid_cmdline), ONE("stat", S_IRUGO, proc_tgid_stat), ONE("statm", S_IRUGO, proc_pid_statm), + ONE("children", S_IRUGO, proc_pid_children), REG("maps", S_IRUGO, proc_maps_operations), #ifdef CONFIG_NUMA REG("numa_maps", S_IRUGO, proc_numa_maps_operations), Index: linux-2.6.git/fs/proc/internal.h =================================================================== --- linux-2.6.git.orig/fs/proc/internal.h +++ linux-2.6.git/fs/proc/internal.h @@ -51,6 +51,9 @@ extern int proc_pid_status(struct seq_fi struct pid *pid, struct task_struct *task); extern int proc_pid_statm(struct seq_file *m, struct pid_namespace *ns, struct pid *pid, struct task_struct *task); +extern int proc_pid_children(struct seq_file *m, struct pid_namespace *ns, + struct pid *pid, struct task_struct *task); + extern loff_t mem_lseek(struct file *file, loff_t offset, int orig); extern const struct file_operations proc_maps_operations;
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