Re: [PATCH 4/16] Change data structures for pid namespaces

[sukadev@us.ibm.com]

Cedric Le Goater [clg@fr.ibm.com] wrote:
| Pavel Emelianov wrote:
| > struct pid_namespace will have the kmem_cache to allocate
| > the pids from, the parent, as they are hierarchical, and
| > the level of nesting value.
| > 
| > struct pid will have a variable length array of pid_number-s
| > one for each namespace this pid lives in. The level value
| > shows the level of the namespace this pid lives in and thus -
| > the number of elements in the numbers array.
| > 
| > Signed-off-by: Pavel Emelianov <xemul@openvz.org>
| > 
| > ---
| > 
| >  include/linux/init_task.h     |    6 ++++++
| >  include/linux/pid.h           |    9 +++++++++
| >  include/linux/pid_namespace.h |    3 +++
| >  kernel/pid.c                  |    3 ++-
| >  4 files changed, 20 insertions(+), 1 deletion(-)
| > 
| > diff -upr linux-2.6.22-rc4-mm2.orig/include/linux/pid.h linux-2.6.22-rc4-mm2-2/include/linux/pid.h
| > --- linux-2.6.22-rc4-mm2.orig/include/linux/pid.h	2007-06-14 12:14:29.000000000 +0400
| > +++ linux-2.6.22-rc4-mm2-2/include/linux/pid.h	2007-07-04 19:00:38.000000000 +0400
| > @@ -40,6 +40,13 @@ enum pid_type
| >   * processes.
| >   */
| > 
| > +struct pid_number {
| > +	/* Try to keep pid_chain in the same cacheline as nr for find_pid */
| > +	int nr;
| > +	struct pid_namespace *ns;
| > +	struct hlist_node pid_chain;
| > +};

We meant to go back and look at removing the extra 'struct pid *' we had
here. Looks like you did that. Cool.

| > +
| >  struct pid
| >  {
| >  	atomic_t count;
| > @@ -40,6 +40,8 @@ enum pid_type
| >  	/* lists of tasks that use this pid */
| >  	struct hlist_head tasks[PIDTYPE_MAX];
| >  	struct rcu_head rcu;
| > +	int level;
| > +	struct pid_number numbers[1];
| >  };
| > 
| >  extern struct pid init_struct_pid;
| > diff -upr linux-2.6.22-rc4-mm2.orig/include/linux/pid_namespace.h linux-2.6.22-rc4-mm2-2/include/linux/pid_namespace.h
| > --- linux-2.6.22-rc4-mm2.orig/include/linux/pid_namespace.h	2007-06-14 12:14:29.000000000 +0400
| > +++ linux-2.6.22-rc4-mm2-2/include/linux/pid_namespace.h	2007-07-04 19:00:39.000000000 +0400
| > @@ -16,7 +15,10 @@ struct pidmap {
| >  	struct kref kref;
| >  	struct pidmap pidmap[PIDMAP_ENTRIES];
| >  	int last_pid;
| > +	int level;
| >  	struct task_struct *child_reaper;
| > +	struct kmem_cache *pid_cachep;
| 
| so, that looks like a good idea to have the cache in the pidmap. could you 
| push that independently to see how it all fits together ?

Yes. I like this idea too.

| 
| thanks,
| 
| C.