Messages in this thread | | | Date | Tue, 1 May 2007 13:37:24 -0700 | From | "Paul Menage" <> | Subject | Re: [ckrm-tech] [PATCH 3/9] Containers (V9): Add tasks file interface |
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On 5/1/07, Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > + if (container_is_removed(cont)) { > > + retval = -ENODEV; > > + goto out2; > > + } > > Can't we make this check prior to kmalloc() and copy_from_user()?
We could but I'm not sure what it would buy us - we'd be optimizing for the case that essentially never occurs.
> > > > > +int container_task_count(const struct container *cont) { > > + int count = 0; > > + struct task_struct *g, *p; > > + struct container_subsys_state *css; > > + int subsys_id; > > + get_first_subsys(cont, &css, &subsys_id); > > + > > + read_lock(&tasklist_lock); > > Can be replaced with rcu_read_lock() and rcu_read_unlock()
Are you sure about that? I see many users of do_each_thread()/while_each_thread() taking a lock on tasklist_lock, and only one (fs/binfmt_elf.c) that's clearly relying on an RCU critical sections. Documentation?
> > Any chance we could get a per-container task list? It will > help subsystem writers as well.
It would be possible, yes - but we probably wouldn't want the overhead (additional ref counts and list manipulations on every fork/exit) of it on by default. We could make it a config option that particular subsystems could select.
I guess the question is how useful is this really, compared to just doing a do_each_thread() and seeing which tasks are in the container? Certainly that's a non-trivial operation, but in what circumstances is it really necessary to do it?
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