Paul Menage wrote:
On 5/1/07, Balbir Singh <[email protected]> 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.
I am not sure about the never occurs part of it, because we check
for the condition, so it could occur. I agree, it is a premature
optimization and could wait a little longer before going in.
> +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?
I suspect they are all pending conversions to be made.
Eric is the expert on this. Meanwhile here's a couple of
pointers. Quoting from the second URL
"We don't need the tasklist_lock to safely iterate through processes
anymore."
http://www.linuxjournal.com/article/6993 (please see incremental use
of RCU) and
http://kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.17/2.6.17-mm2/broken-out/proc-remove-tasklist_lock-from-proc_pid_readdir.patch
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?
Paul
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
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