linux-kernel - Re: Testing for dirty buffers on a block device

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Message-ID: <20100225082035.GR1025@kernel.dk>
Date:	Thu, 25 Feb 2010 09:20:35 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	linux-pm <linux-pm@...ts.linux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Testing for dirty buffers on a block device

On Wed, Feb 24 2010, Alan Stern wrote:
> On Wed, 24 Feb 2010, Jens Axboe wrote:
> 
> > > > But if you wanted, I guess the only way would be to lookup
> > > > dirty/writeback pages on the bdev inode mapping. For that you'd need the
> > > > bdev, not the gendisk or the queue though.
> > > 
> > > I can get the bdev from the gendisk by calling bdget_disk() with a 
> > > partition number of 0, right?  What would the next step be?  Would this 
> > > check for dirty pages associated with any of the partitions or would it 
> > > only look at pages associated with the inode for the entire disk?
> > 
> > It would cover the entire bdev.
> 
> Okay, so once I've got the bdev, how do I look up the dirty/writeback 
> pages on the inode mapping?

I _think_ you can get away with not doing a radix lookup for dirty
pages, just looking at the BDI_RECLAIMABLE stat on the bdi. That would
be:

bdi_stat(bdev->bd_inode->i_mapping->backing_dev_info, BDI_RECLAIMABLE);

-- 
Jens Axboe

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