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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 26 Feb 2010 09:19:04 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	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 Thu, Feb 25, 2010 at 09:20:35AM +0100, Jens Axboe wrote:
> 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);

mapping_tagged(bdev->bd_inode->i_mapping, PAGECACHE_TAG_DIRTY);

is about as low overhead as it gets as the radix tree propagateѕ
tags back up to the root. i.e. no page lookups needed at all to
determine if it is dirty.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/