On Tue, Jul 07, 2009 at 09:40:14AM +0800, Gui Jianfeng wrote:
> Get rid of css id from io cgroup since it's nothing
> more than keeping track of iocg. An alternative is
> caching iocg pointer in io group, just remove the
> complexity.
>
Gui, one advantage of using css_id is that we store only 2 bytes of id
instead of 8 bytes of iocg* pointer (on 64bit). So saving of 6 bytes per
group. May be it is not a bad idea to keep the usage of css id around
because anyway we don't seem to gain much by getting rid of it.
So for the time being I tend to think that lets continue using css id.
Thanks
Vivek
> Signed-off-by: Gui Jianfeng <guijianfeng@xxxxxxxxxxxxxx>
> ---
> block/elevator-fq.c | 36 ++++++++++++------------------------
> block/elevator-fq.h | 2 +-
> 2 files changed, 13 insertions(+), 25 deletions(-)
>
> diff --git a/block/elevator-fq.c b/block/elevator-fq.c
> index 7c83d1e..f499b54 100644
> --- a/block/elevator-fq.c
> +++ b/block/elevator-fq.c
> @@ -191,25 +191,19 @@ static inline struct io_group *iog_parent(struct io_group *iog)
> #ifdef CONFIG_DEBUG_GROUP_IOSCHED
> static void io_group_path(struct io_group *iog, char *buf, int buflen)
> {
> - unsigned short id = iog->iocg_id;
> - struct cgroup_subsys_state *css;
> + struct io_cgroup *iocg;
> + int ret;
>
> rcu_read_lock();
>
> - if (!id)
> + iocg = iog->iocg;
> + if (!iocg)
> goto out;
>
> - css = css_lookup(&io_subsys, id);
> - if (!css)
> - goto out;
> -
> - if (!css_tryget(css))
> + ret = cgroup_path(iocg->css.cgroup, buf, buflen);
> + if (ret)
> goto out;
>
> - cgroup_path(css->cgroup, buf, buflen);
> -
> - css_put(css);
> -
> rcu_read_unlock();
> return;
> out:
> @@ -1847,7 +1841,6 @@ struct cgroup_subsys io_subsys = {
> .destroy = iocg_destroy,
> .populate = iocg_populate,
> .subsys_id = io_subsys_id,
> - .use_id = 1,
> };
>
> static inline unsigned int iog_weight(struct io_group *iog)
> @@ -1890,7 +1883,7 @@ io_group_chain_alloc(struct request_queue *q, void *key, struct cgroup *cgroup)
> if (!iog)
> goto cleanup;
>
> - iog->iocg_id = css_id(&iocg->css);
> + iog->iocg = iocg;
>
> sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
> iog->dev = MKDEV(major, minor);
> @@ -2201,7 +2194,7 @@ static struct io_group *io_alloc_root_group(struct request_queue *q,
> spin_lock_irq(&iocg->lock);
> rcu_assign_pointer(iog->key, key);
> hlist_add_head_rcu(&iog->group_node, &iocg->group_data);
> - iog->iocg_id = css_id(&iocg->css);
> + iog->iocg = iocg;
> spin_unlock_irq(&iocg->lock);
>
> #ifdef CONFIG_DEBUG_GROUP_IOSCHED
> @@ -2397,7 +2390,7 @@ remove_entry:
> group_node);
> efqd = rcu_dereference(iog->key);
> hlist_del_rcu(&iog->group_node);
> - iog->iocg_id = 0;
> + iog->iocg = NULL;
> spin_unlock_irqrestore(&iocg->lock, flags);
>
> spin_lock_irqsave(efqd->queue->queue_lock, flags);
> @@ -2411,7 +2404,6 @@ done:
> kfree(pn);
> }
>
> - free_css_id(&io_subsys, &iocg->css);
> rcu_read_unlock();
> BUG_ON(!hlist_empty(&iocg->group_data));
> kfree(iocg);
> @@ -2427,20 +2419,16 @@ static void io_group_check_and_destroy(struct elv_fq_data *efqd,
> {
> struct io_cgroup *iocg;
> unsigned long flags;
> - struct cgroup_subsys_state *css;
>
> rcu_read_lock();
>
> - css = css_lookup(&io_subsys, iog->iocg_id);
> -
> - if (!css)
> + iocg = iog->iocg;
> + if (!iocg)
> goto out;
>
> - iocg = container_of(css, struct io_cgroup, css);
> -
> spin_lock_irqsave(&iocg->lock, flags);
>
> - if (iog->iocg_id) {
> + if (iog->iocg) {
> hlist_del_rcu(&iog->group_node);
> __io_destroy_group(efqd, iog);
> }
> diff --git a/block/elevator-fq.h b/block/elevator-fq.h
> index f089a55..75fee82 100644
> --- a/block/elevator-fq.h
> +++ b/block/elevator-fq.h
> @@ -251,7 +251,7 @@ struct io_group {
> unsigned int busy_rt_queues;
>
> int deleting;
> - unsigned short iocg_id;
> + struct io_cgroup *iocg;
>
> /* The device MKDEV(major, minor), this group has been created for */
> dev_t dev;
> --
> 1.5.4.rc3
>
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