linux-kernel - Re: [PATCH 1/1] Add check for dirty_writeback_interval in bdi_wakeup_thread

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Date:	Mon, 18 Apr 2011 10:19:12 +0300
From:	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
To:	Raghavendra D Prabhu <rprabhu@...hang.net>
Cc:	linux-mm@...ck.org, Jens Axboe <jaxboe@...ionio.com>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Add check for dirty_writeback_interval in
 bdi_wakeup_thread_delayed

On Sun, 2011-04-17 at 21:53 +0530, Raghavendra D Prabhu wrote:
> In the function bdi_wakeup_thread_delayed, no checks are performed on
> dirty_writeback_interval unlike other places and timeout is being set to
> zero as result, thus defeating the purpose. So, I have changed it to be
> passed default value of interval which is 500 centiseconds, when it is
> set to zero.
> I have also verified this and tested it.
> 
> Signed-off-by: Raghavendra D Prabhu <rprabhu@...hang.net>

If  dirty_writeback_interval then the periodic write-back has to be
disabled. Which means we should rather do something like this:

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 0d9a036..f38722c 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -334,10 +334,12 @@ static void wakeup_timer_fn(unsigned long data)
  */
 void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
 {
-       unsigned long timeout;
+       if (dirty_writeback_interval) {
+               unsigned long timeout;
 
-       timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
-       mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
+               timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
+               mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
+       }
 }

I do not see why you use 500 centisecs instead - I think this is wrong.

> ---
>   mm/backing-dev.c |    5 ++++-
>   1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index befc875..d06533c 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -336,7 +336,10 @@ void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi)
>   {
>   	unsigned long timeout;
>   
> -	timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
> +	if (dirty_writeback_interval)
> +		timeout = msecs_to_jiffies(dirty_writeback_interval * 10);
> +	else
> +		timeout = msecs_to_jiffies(5000);
>   	mod_timer(&bdi->wb.wakeup_timer, jiffies + timeout);
>   }
>   


-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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