linux-kernel - Re: [PATCH] workqueue: don't alloc

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Date:	Wed, 21 Jan 2009 11:29:30 +0100
From:	Frédéric Weisbecker <fweisbec@...il.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Oleg Nesterov <oleg@...sign.ru>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] workqueue: don't alloc_percpu for single workqueue

2009/1/21 Lai Jiangshan <laijs@...fujitsu.com>:
>
> allocating memory for every cpu for single workqueue is waste.
>
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 2f44583..ecd693d 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -99,7 +99,7 @@ static
>  struct cpu_workqueue_struct *wq_per_cpu(struct workqueue_struct *wq, int cpu)
>  {
>        if (unlikely(is_wq_single_threaded(wq)))
> -               cpu = singlethread_cpu;
> +               return wq->cpu_wq;
>        return per_cpu_ptr(wq->cpu_wq, cpu);
>  }
>
> @@ -417,7 +417,7 @@ void flush_workqueue(struct workqueue_struct *wq)
>        lock_map_acquire(&wq->lockdep_map);
>        lock_map_release(&wq->lockdep_map);
>        for_each_cpu_mask_nr(cpu, *cpu_map)
> -               flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
> +               flush_cpu_workqueue(wq_per_cpu(wq, cpu));
>  }
>  EXPORT_SYMBOL_GPL(flush_workqueue);
>
> @@ -548,7 +548,7 @@ static void wait_on_work(struct work_struct *work)
>        cpu_map = wq_cpu_map(wq);
>
>        for_each_cpu_mask_nr(cpu, *cpu_map)
> -               wait_on_cpu_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
> +               wait_on_cpu_work(wq_per_cpu(wq, cpu), work);
>  }
>
>  static int __cancel_work_timer(struct work_struct *work,
> @@ -752,17 +752,13 @@ int current_is_keventd(void)
>
>  }
>
> -static struct cpu_workqueue_struct *
> -init_cpu_workqueue(struct workqueue_struct *wq, int cpu)
> +static void init_cpu_workqueue(struct workqueue_struct *wq,
> +               struct cpu_workqueue_struct *cwq)
>  {
> -       struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
> -
>        cwq->wq = wq;
>        spin_lock_init(&cwq->lock);
>        INIT_LIST_HEAD(&cwq->worklist);
>        init_waitqueue_head(&cwq->more_work);
> -
> -       return cwq;
>  }
>
>  static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
> @@ -816,7 +812,10 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
>        if (!wq)
>                return NULL;
>
> -       wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
> +       if (singlethread)
> +               wq->cpu_wq = kmalloc(sizeof(*cwq), GFP_KERNEL);
> +       else
> +               wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
>        if (!wq->cpu_wq) {
>                kfree(wq);
>                return NULL;
> @@ -830,7 +829,8 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
>        INIT_LIST_HEAD(&wq->list);
>
>        if (singlethread) {
> -               cwq = init_cpu_workqueue(wq, singlethread_cpu);
> +               cwq = wq->cpu_wq;
> +               init_cpu_workqueue(wq, cwq);
>                err = create_workqueue_thread(cwq, singlethread_cpu);
>                start_workqueue_thread(cwq, -1);
>        } else {
> @@ -851,7 +851,8 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
>                 * lock.
>                 */
>                for_each_possible_cpu(cpu) {
> -                       cwq = init_cpu_workqueue(wq, cpu);
> +                       cwq = per_cpu_ptr(wq->cpu_wq, cpu);
> +                       init_cpu_workqueue(wq, cwq);
>                        if (err || !cpu_online(cpu))
>                                continue;
>                        err = create_workqueue_thread(cwq, cpu);
> @@ -906,6 +907,13 @@ void destroy_workqueue(struct workqueue_struct *wq)
>        const struct cpumask *cpu_map = wq_cpu_map(wq);
>        int cpu;
>
> +       if (is_wq_single_threaded(wq)) {
> +               cleanup_workqueue_thread(wq->cpu_wq);
> +               kfree(wq->cpu_wq);
> +               kfree(wq);
> +               return;
> +       }
> +
>        cpu_maps_update_begin();
>        spin_lock(&workqueue_lock);
>        list_del(&wq->list);
>


Looks like a nice catch!
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