[LSF/MM][ATTEND]filesystem -- reflink

[LSF/MM][ATTEND]filesystem -- reflink

[mingming cao]

Hello,

I'd like to attend Linux storage and filesystem summit. I am interested 
in discussion of general lockless direct io and more interested in 
discussion of reflink support for filesystem. Btrfs and OCFS2 has this 
support, My goal is explore what's best to way this support for ext4. 
If there is any crossover work between filesystem and vfs people, or 
filesystem and dm layer I am more than happy to discuss about it too.

Thanks,
Mingming

Re: [Lsf-pc] [LSF/MM][ATTEND]filesystem -- reflink

[Jan Kara]

  Hello,

On Tue 14-01-14 23:16:20, mingming cao wrote:
> I'd like to attend Linux storage and filesystem summit. I am
> interested in discussion of general lockless direct io and more
> interested in discussion of reflink support for filesystem. Btrfs
> and OCFS2 has this support, My goal is explore what's best to way
> this support for ext4. If there is any crossover work between
> filesystem and vfs people, or filesystem and dm layer I am more than
> happy to discuss about it too.
  There was a project for implementing COW for ext4 but it was a really
major surgery and in the end didn't get to an upstreamable state. Reflink
is somewhat simpler than general COW because it's only about fs data. In
particular implementing reflink with a file granularity (i.e., a type of
hardlink which is automatically converted to a copy when first opened for
writing) is relatively simple to do but I'm not sure how useful it is.
Doing reflink properly with block granularity is harder with block
refcounting etc.

Do you have any particular usecase in mind?

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

Re: [Lsf-pc] [LSF/MM][ATTEND]filesystem -- reflink

[Dave Chinner]

On Wed, Jan 15, 2014 at 10:03:12AM +0100, Jan Kara wrote:
>   Hello,
> 
> On Tue 14-01-14 23:16:20, mingming cao wrote:
> > I'd like to attend Linux storage and filesystem summit. I am
> > interested in discussion of general lockless direct io and more
> > interested in discussion of reflink support for filesystem. Btrfs
> > and OCFS2 has this support, My goal is explore what's best to way
> > this support for ext4. If there is any crossover work between
> > filesystem and vfs people, or filesystem and dm layer I am more than
> > happy to discuss about it too.
>   There was a project for implementing COW for ext4 but it was a really
> major surgery and in the end didn't get to an upstreamable state. Reflink
> is somewhat simpler than general COW because it's only about fs data. In
> particular implementing reflink with a file granularity (i.e., a type of
> hardlink which is automatically converted to a copy when first opened for
> writing) is relatively simple to do but I'm not sure how useful it is.
> Doing reflink properly with block granularity is harder with block
> refcounting etc.
> 
> Do you have any particular usecase in mind?

The use case I keep hearing for reflink in XFS is optimising
distributed filesystem snapshot implementations, which tend to
require file block level COW semantics on a per-file basis...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com