linux-ext4 - Re: [PATCH v4 0/3] dioread

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Date:	Fri, 15 Jan 2010 14:39:48 -0500
From:	Ric Wheeler <rwheeler@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
CC:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Chris Mason <chris.mason@...cle.com>
Subject: Re: [PATCH v4 0/3] dioread_nolock patch

On 01/15/2010 02:30 PM, Theodore Ts'o wrote:
> I've worked with Jiaying to ready this patch for submission.
>
> It's currently a mount option for maximum safety, but after we do some
> benchmarking to make sure it doesn't degrade performance for buffered
> writes, we may want to make this the default.  Once really nice side
> effect of this patch is that it effectively gives us "guarded mode" by
> default, since the blocks are marked as uninitialized and only converted
> to be initialized when the I/O has completed for both buffered and
> direct I/O writes now.  This means that we could possibly change the
> default mode to be data=writeback if the extents feature is enabled,
> since data=ordered would only needed for safety when writing new
> old-style indirect blocks.
>
> The plan is to merge this for 2.6.34.  I've looked this over pretty
> carefully, but another pair of eyes would be appreciated, especially if
> we make this the default.  Beyond the advantages of being able to use
> data=writeback, I believe this should be a major win for database
> workloads.
>
> 					- Ted
>    

I would be really cautious about turning this on unless we are 100% 
certain that we have not introduced data integrity issues. Performance 
testing is great, but we need to work hard on the power failure testing, 
etc as well....

What ever did happen to guarded mode? Is it still lurking out there?

ric


> Theodore Ts'o (3):
>    ext4: mechanical change on dio get_block code in prepare for it to be
>      used by buffer write
>    ext4: use ext4_get_block_write in buffer write
>    ext4: Use direct_IO_no_locking in ext4 dio read.
>
>   fs/ext4/ext4.h      |   28 +++++---
>   fs/ext4/ext4_jbd2.h |   24 +++++++
>   fs/ext4/extents.c   |   36 +++++-----
>   fs/ext4/fsync.c     |    2 +-
>   fs/ext4/inode.c     |  192 +++++++++++++++++++++++++++++++++-----------------
>   fs/ext4/super.c     |   32 +++++++--
>   6 files changed, 217 insertions(+), 97 deletions(-)
>
> --
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