From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: [PATCH 1/2] writeback: Improve busyloop prevention
Date: Thu, 8 Sep 2011 08:57:50 +0800
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Cc: "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@infradead.org>
To: Jan Kara <jack@suse.cz>
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On Thu, Sep 08, 2011 at 08:44:43AM +0800, Jan Kara wrote:
> Writeback of an inode can be stalled by things like internal fs locks being
> held. So in case we didn't write anything during a pass through b_io list,
> just wait for a moment and try again.
 
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>

with comments below.

> +		trace_writeback_wait(wb->bdi, work);
> +		spin_unlock(&wb->list_lock);

__set_current_state(TASK_INTERRUPTIBLE);

> +		schedule_timeout(pause);

> +		pause <<= 1;
> +		if (pause > HZ / 10)
> +			pause = HZ / 10;

It's a bit more safer to do

                if (pause < HZ / 10)
                        pause <<= 1;

in case someone hacked HZ=1.

Thanks,
Fengguang