From: Christoph Hellwig <hch@infradead.org>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Christoph Hellwig <hch@infradead.org>,
Michael Tokarev <mjt@tls.msk.ru>, KVM list <kvm@vger.kernel.org>,
Kevin Wolf <kwolf@redhat.com>
Subject: Re: JFYI: ext4 bug triggerable by kvm
Date: Tue, 17 Aug 2010 05:07:55 -0400 [thread overview]
Message-ID: <20100817090755.GA11110@infradead.org> (raw)
In-Reply-To: <4C69A0C4.2080102@codemonkey.ws>
On Mon, Aug 16, 2010 at 03:34:12PM -0500, Anthony Liguori wrote:
> On 08/16/2010 01:42 PM, Christoph Hellwig wrote:
> >On Mon, Aug 16, 2010 at 09:43:09AM -0500, Anthony Liguori wrote:
> >>>Also, ext4 is _very_ slow on O_SYNC writes (which is
> >>>used in kvm with default cache).
> >>Yeah, we probably need to switch to sync_file_range() to avoid the
> >>journal commit on every write.
> >>
> >No, we don't. sync_file_range does not actually provide any data
> >integrity.
>
> What do you mean by data integrity?
sync_file_range only does pagecache-level writeout of the file data.
It nevers calls into the actual filesystem, that means any block
allocations (for filling holes / converting preallocated space in normal
filesystems, or every write in COW-based filesstems like qcow2) never
get flushes to disk, and even more importantly the disk write cache is
never flushed.
In short it's completely worthless for any real filesystem.
next prev parent reply other threads:[~2010-08-17 9:07 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-16 14:00 JFYI: ext4 bug triggerable by kvm Michael Tokarev
2010-08-16 14:43 ` Anthony Liguori
2010-08-16 18:42 ` Christoph Hellwig
2010-08-16 20:34 ` Anthony Liguori
2010-08-17 9:07 ` Christoph Hellwig [this message]
2010-08-17 9:23 ` Avi Kivity
2010-08-17 11:17 ` Christoph Hellwig
2010-08-17 12:56 ` Anthony Liguori
2010-08-17 13:07 ` Christoph Hellwig
2010-08-17 14:20 ` Anthony Liguori
2010-08-17 14:28 ` Christoph Hellwig
2010-08-17 14:39 ` Anthony Liguori
2010-08-17 14:45 ` Christoph Hellwig
2010-08-17 14:53 ` Avi Kivity
2010-08-17 14:54 ` Anthony Liguori
2010-08-17 15:01 ` Avi Kivity
2010-08-17 15:02 ` Christoph Hellwig
2010-08-17 14:40 ` Michael Tokarev
2010-08-17 14:44 ` Anthony Liguori
2010-08-17 14:46 ` Christoph Hellwig
2010-08-17 14:57 ` Anthony Liguori
2010-08-17 14:59 ` Avi Kivity
2010-08-17 15:04 ` Christoph Hellwig
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