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Message-ID: <CAEH94LjoanfL3piP89qM6MP6zdN0AybfeqJe0kR_5-DJ0mLH_w@mail.gmail.com>
Date: Wed, 17 Oct 2012 14:34:15 +0800
From: Zhi Yong Wu <zwu.kernel@...il.com>
To: Dave Chinner <david@...morbit.com>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
linuxram@...ux.vnet.ibm.com, viro@...iv.linux.org.uk,
dave@...os.cz, tytso@....edu, cmm@...ibm.com,
Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [RFC v3 09/13] vfs: add one wq to update map info periodically
On Tue, Oct 16, 2012 at 8:27 AM, Dave Chinner <david@...morbit.com> wrote:
> On Wed, Oct 10, 2012 at 06:07:31PM +0800, zwu.kernel@...il.com wrote:
>> From: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
>>
>> Add a per-superblock workqueue and a work_struct
>> to run periodic work to update map info on each superblock.
>>
>> Signed-off-by: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
>> ---
>> fs/hot_tracking.c | 94 ++++++++++++++++++++++++++++++++++++++++++
>> fs/hot_tracking.h | 3 +
>> include/linux/hot_tracking.h | 2 +
>> 3 files changed, 99 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/hot_tracking.c b/fs/hot_tracking.c
>> index a8dc599..f333c47 100644
>> --- a/fs/hot_tracking.c
>> +++ b/fs/hot_tracking.c
>> @@ -15,6 +15,8 @@
>> #include <linux/module.h>
>> #include <linux/spinlock.h>
>> #include <linux/hardirq.h>
>> +#include <linux/kthread.h>
>> +#include <linux/freezer.h>
>> #include <linux/fs.h>
>> #include <linux/blkdev.h>
>> #include <linux/types.h>
>> @@ -623,6 +625,88 @@ static void hot_map_array_exit(struct hot_info *root)
>> }
>>
>> /*
>> + * Update temperatures for each hot inode item and
>> + * hot range item for aging purposes
>> + */
>> +static void hot_temperature_update_work(struct work_struct *work)
>> +{
>> + struct hot_update_work *hot_work =
>> + container_of(work, struct hot_update_work, work);
>> + struct hot_info *root = hot_work->hot_info;
>> + struct hot_inode_item *hi_nodes[8];
>> + unsigned long delay = HZ * HEAT_UPDATE_DELAY;
>> + u64 ino = 0;
>> + int i, n;
>> +
>> + do {
>> + while (1) {
>> + spin_lock(&root->lock);
>> + n = radix_tree_gang_lookup(&root->hot_inode_tree,
>> + (void **)hi_nodes, ino,
>> + ARRAY_SIZE(hi_nodes));
>> + if (!n) {
>> + spin_unlock(&root->lock);
>> + break;
>> + }
>> +
>> + ino = hi_nodes[n - 1]->i_ino + 1;
>> + for (i = 0; i < n; i++) {
>> + kref_get(&hi_nodes[i]->hot_inode.refs);
>> + hot_map_array_update(
>> + &hi_nodes[i]->hot_inode.hot_freq_data, root);
>> + hot_range_update(hi_nodes[i], root);
>> + hot_inode_item_put(hi_nodes[i]);
>> + }
>> + spin_unlock(&root->lock);
>
> This is a lot of work to do under a spin lock. Perhaps you should
> get a reference on all the nodes, then drop the root->lock and then
> update all the nodes in a separate loop.
OK, done
>
>> + }
>> +
>> + if (unlikely(freezing(current))) {
>> + __refrigerator(true);
>> + } else {
>> + set_current_state(TASK_INTERRUPTIBLE);
>> + if (!kthread_should_stop()) {
>> + schedule_timeout(delay);
>> + }
>> + __set_current_state(TASK_RUNNING);
>> + }
>> + } while (!kthread_should_stop());
>
> I don't think you understand workqueues fully. A work queue worker
> function is not something that executes endlessly. It is a
> "one-shot" function that does the work once, not an endless loop
> that has to delay it's execution for periodic work.
ah, i have done this based on your following suggestions, thanks.
>
> If you need periodic work, then you should use a struct delayed_work
> and queue the next work iteration to be run a later time. See, for
> example, xfs_syncd_worker() and xfs_syncd_queue_sync() and how that
> reschedules itself for periodic work. It also means you don't have
> to handle kthread freezing, as the WQ infrastructure takes care of
> that for you.
ditto.
>
> This is why unmount is hanging for me - this work never completes,
> so flush_workqueue() will never return.
got it, thanks.
>
>> +}
>> +
>> +static int hot_wq_init(struct hot_info *root)
>> +{
>> + struct hot_update_work *hot_work;
>> + int ret = 0;
>> +
>> + root->update_wq = alloc_workqueue(
>> + "hot_temperature_update", WQ_MEM_RECLAIM | WQ_UNBOUND, 1);
>> + if (!root->update_wq) {
>> + printk(KERN_ERR "%s: failed to create "
>> + "temperature update workqueue\n",
>> + __func__);
>> + return 1;
>> + }
>> +
>> + hot_work = kmalloc(sizeof(*hot_work), GFP_NOFS);
>> + if (hot_work) {
>> + hot_work->hot_info = root;
>> + INIT_WORK(&hot_work->work, hot_temperature_update_work);
>> + queue_work(root->update_wq, &hot_work->work);
>> + } else {
>> + printk(KERN_ERR "%s: failed to create update work\n",
>> + __func__);
>> + ret = 1;
>> + }
>
> I don't understand why you need a separate "hot_work" structure.
> just embed a struct delayed_work in the struct hot_info and use
> container_of() to get the struct hot_info from the work structure.
> As such, there's no need for a separate function just for this
> initialisation - just put it in line.
OK, done.
>
>> +
>> + return ret;
>> +}
>> +
>> +static void hot_wq_exit(struct workqueue_struct *wq)
>> +{
>> + flush_workqueue(wq);
>
> flush_workqueue_sync().
done, thanks
>
>> + destroy_workqueue(wq);
>> +}
>
> And there's not need for separate function for this - put it in
> line.
ditto.
>
> FWIW, it also leaks the hot_work structure, but you're going to
> remove that anyway. ;)
>
>> diff --git a/fs/hot_tracking.h b/fs/hot_tracking.h
>> index d19e64a..7a79a6d 100644
>> --- a/fs/hot_tracking.h
>> +++ b/fs/hot_tracking.h
>> @@ -36,6 +36,9 @@
>> */
>> #define TIME_TO_KICK 400
>>
>> +/* set how often to update temperatures (seconds) */
>> +#define HEAT_UPDATE_DELAY 400
>
> FWIW, 400 seconds is an unusual time period. It's expected that
> periodic work might take place at intervals of 5 minutes, 10
> minutes, etc, not 6m40s. It's much easier to predict and understand
> behaviour if it's at a interval of whole units like minutes,
> especially when looking at timestamped event traces. Hence 300s (5
> minutes) makes a lot more sense as a period for updates...
got it. thanks.
>
>> /*
>> * The following comments explain what exactly comprises a unit of heat.
>> *
>> diff --git a/include/linux/hot_tracking.h b/include/linux/hot_tracking.h
>> index 7114179..b37e0f8 100644
>> --- a/include/linux/hot_tracking.h
>> +++ b/include/linux/hot_tracking.h
>> @@ -84,6 +84,8 @@ struct hot_info {
>>
>> /* map of range temperature */
>> struct hot_map_head heat_range_map[HEAT_MAP_SIZE];
>> +
>> + struct workqueue_struct *update_wq;
>
> Add the struct delayed_work here, too.
ditto
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@...morbit.com
--
Regards,
Zhi Yong Wu
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