Re: [PATCH v2 1/2] pid: Replace pid bitmap implementation with IDR API

Oleg Nesterov
2017-09-27T15:06:00Z

On 09/27, Gargi Sharma wrote:
>
> @@ -309,7 +168,22 @@ struct pid *alloc_pid(struct pid_namespace *ns)
> tmp = ns;
> pid->level = ns->level;
> for (i = ns->level; i >= 0; i--) {
> - nr = alloc_pidmap(tmp);
> + int pid_min = 1;
> + idr_preload(GFP_KERNEL);
> + spin_lock_irq(&pidmap_lock);
> +
> + /*
> + * init really needs pid 1, but after reaching the maximum
> + * wrap back to RESERVED_PIDS
> + */
> + if (tmp->idr.idr_next > RESERVED_PIDS)
> + pid_min = RESERVED_PIDS;
> +
> + nr = idr_alloc_cyclic(&tmp->idr, pid, pid_min,
> + pid_max, GFP_ATOMIC);
> + spin_unlock_irq(&pidmap_lock);
> + idr_preload_end();
> +
> if (nr < 0) {
> retval = nr;
> goto out_free;
> @@ -346,12 +220,14 @@ struct pid *alloc_pid(struct pid_namespace *ns)
> return pid;
>
> out_unlock:
> - spin_unlock_irq(&pidmap_lock);
> put_pid_ns(ns);
> + spin_unlock_irq(&pidmap_lock);

Why? No need to move put_pid_ns() under pidmap_lock, please remove this change...

> void __init pidhash_init(void)
> {
> + unsigned int pidhash_size;
> +
> pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18,
> HASH_EARLY | HASH_SMALL | HASH_ZERO,
> &pidhash_shift, NULL,
> 0, 4096);
> + pidhash_size = 1U << pidhash_shift;
> }

Hmm, this change makes no sense. And the next patch kills pidhash_init()
altogether.

Oleg.