linux-kernel - Re: [RFC v2 07/10] vfs: fork one kthread to update data temperature

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Date:	Thu, 27 Sep 2012 14:54:22 +0800
From:	Zhi Yong Wu <zwu.kernel@...il.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
	linuxram@...ux.vnet.ibm.com, viro@...iv.linux.org.uk,
	cmm@...ibm.com, tytso@....edu, marco.stornelli@...il.com,
	stroetmann@...olinux.com, diegocg@...il.com, chris@...muel.org,
	Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [RFC v2 07/10] vfs: fork one kthread to update data temperature

On Thu, Sep 27, 2012 at 12:03 PM, Dave Chinner <david@...morbit.com> wrote:
> On Sun, Sep 23, 2012 at 08:56:32PM +0800, zwu.kernel@...il.com wrote:
>> From: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
>>
>>   Fork and run one kernel kthread to calculate
>> that temperature based on some metrics kept
>> in custom frequency data structs, and store
>> the info in the hash table.
>
> No new kthreads, please. Use a per-superblock workqueue and a struct
> delayed_work to run periodic work on each superblock.
If no new kthread is created, which kthread will work on these
delayed_work tasks?

>
> That will also remove all the nasty, nasty
> !hot_track_temperature_update_kthread checks from the code, too.
>
> Also, I'd separate the work that the workqueue does from the patch
> that introduces the work queue. That way there is only one new thing
> to comment on in the patch. Further, I'd separate the aging code
> from the code that updates the temperature map into it's own patch
> as well..
>
> Finally, you're going to need a shrinker to control the amount of
> memory that is used in tracking hot regions - if we are throwing
> inodes out of memory due to memory pressure, we most definitely are
> going to need to reduce the amount of memory the tracking code is
> using, even if it means losing useful information (i.e. the shrinker
> accelerates the aging process).
Great, I agree with you.
>
> Given the above, and the other comments earlier in the series,
> there's not a lot of point in me spending time commenting on ethe
> code in detail here as it will change significantly as a result of
> all the earlier comments....
OK,  i will complete the code change based on all your earlier comments ASAP.
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@...morbit.com
> --
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-- 
Regards,

Zhi Yong Wu
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