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

[Qu WenRuo <wqu@suse.com>]

On 2019/10/16 下午7:16, David Sterba wrote:
> 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.

That's interesting.

And indeed, since we're dealing one less tree, there is no chance to
cause the bug mentioned by Josef.
> 
>> 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.

That's great!

As long as we're pushing a solution to the mount time problem, I can't
be more happier!

Then I guess no matter which version get merged to upstream, the
patchset is already meaningful.

Thanks,
Qu