Re: [PATCH v2 0/7] btrfs-progs: Support for BG_TREE feature

[David Sterba <dsterba@suse.cz>]

On Tue, Oct 15, 2019 at 08:32:30AM +0800, Qu Wenruo wrote:
> > Have we settled the argument whether to use a new tree or key tricks for
> > the blocgroup data? I think we have not and will read the previous
> > discussions. For a feature like this I want to be sure we understand all
> > the pros and cons.
> > 
> Yep, we haven't settled on the whether creating a new tree, or
> re-organize the keys.
> 
> But as my last discussion said, I see no obvious pro using the existing
> extent tree to hold the new block group item keys, even we can pack them
> all together.

For me the obvious pro is minimum change to existing set of trees.

> And for backup roots, indeed I forgot to add this feature.
> But to me that's a minor point, not a show stopper.
>
> The most important aspect to me is, to allow real world user of super
> large fs to try this feature, to prove the usefulness of this design,
> other than my on-paper analyse.
> 
> That's why I'm pushing the patchset, even it may not pass any review.
> I just want to hold a up-to-date branch so that when some one needs, it
> can grab and try them themselves.

Ok that's fine and I can add the branch to for-next for ease of testing.
I'm working on a prototype that does it the bg item key way, it compiles
and creates almost correct filesystem, so I have to fix it before
posting. The patches are on top of your bg-tree feature so we could have
both in the same kernel for testing.