Re: [REGRESSION] Super slow balance in v5.0-rc1

David Sterba
2019-01-14T09:35:35Z

On Mon, Jan 14, 2019 at 01:39:46PM +0800, Qu Wenruo wrote:
> Hi,
>
> When rebasing my qgroup + balance optimization patches, I found one very
> obvious performance regression for balance.
>
> For normal 4G subvolume, 16 snapshots, balance workload, v4.20 kernel
> only takes 3s to relocate a metadata block group, while for v5.0-rc1, I
> don't really know how it will take as it hasn't finished yet.

This looks like a lockup, unbounded waiting or missed wakeup.

> And the most important part is, this happens when quota is *DISABLED*!!!
>
> I'm bisecting for this regression, but if there are some users trying
> latest rc kernel, please be aware of this regression.

The rc1 can go pretty wild and issues could be caused by other
subsystems, so I'd try to test the merged (32ee34eddad13cd4) and
non-merged (52042d8e82ff50d) branches, this should tell you if it's a
genuine btrfs bug or not.