linux-kernel - Re: [PATCH 26/30] ext4: do not send discards as barriers

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Date:	Fri, 10 Sep 2010 00:53:13 +0200
From:	Jan Kara <jack@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jan Kara <jack@...e.cz>, Jeff Moyer <jmoyer@...hat.com>,
	Christoph Hellwig <hch@....de>, jaxboe@...ionio.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org,
	linux-raid@...r.kernel.org, James.Bottomley@...e.de, tytso@....edu,
	chris.mason@...cle.com, swhiteho@...hat.com,
	konishi.ryusuke@....ntt.co.jp, dm-devel@...hat.com, vst@...b.net,
	rwheeler@...hat.com, hare@...e.de, neilb@...e.de,
	rusty@...tcorp.com.au, mst@...hat.com, jeremy@...p.org,
	snitzer@...hat.com, k-ueda@...jp.nec.com,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 26/30] ext4: do not send discards as barriers

On Tue 31-08-10 10:11:34, Tejun Heo wrote:
> On 08/30/2010 10:20 PM, Jan Kara wrote:
> >   My setup is that I have a dedicated partition / drive for a filesystem
> > which is written to from a guest kernel running under KVM. I have set it up
> > using virtio driver with cache=writeback so that the host caches the writes
> > in a similar way disk caches them. At some point I just kill the qemu-kvm
> > process and at that point I'd like to also throw away data cached by the
> > host...
> 
> $ echo 1 > /sys/block/sdX/device/delete
> $ echo - - - > /sys/class/scsi_host/hostX/scan
> 
> should do the trick.
  I've tested that when mounting with barrier=0 option inside KVM, this indeed
does destroy the filesystem rather badly. With the barrier option, ext4 has
already survived several crash cycles while running fsstress with
journal_async_commit option. So the patch seems to work as expected.

									Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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