Re: [PATCH 6.10 0/3] btrfs: some fixes/updates for the extent map shrinker

[David Sterba <dsterba@suse.cz>]

On Mon, Jul 08, 2024 at 03:42:42PM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> A few fixes for the extent map shrinker that fix some reports from users
> where their desktops became very unresponsive.
> 
> Several notes here:
> 
> 1) The first patch was already sent before to the list and it's in
>    for-next already. It's unrelated to the reports from those users but
>    it's related to a report from syzbot for a deadlock in case the
>    shrinker does an iput on an inode with 0 links that needs to be
>    deleted, and when the inode still has links but it's dirty, it can
>    make the iput wait for writeback to complete, slowing down the
>    shrinker. I've included it here just to group things in a logical
>    way;
> 
> 2) These patches apply to 6.10-rc;
> 
> 3) At least the first 2 patches should go to 6.10 final IMO;
> 
> 4) In case they land in 6.10-rc, then for-next needs to be rebased since
>    there are minor and trivial conflicts to solve due to the last patch in
>    for-next that reduces the size of struct btrfs_inode down to 1024 bytes.
> 
>    Also the following patch which landed on for-next should be dropped
>    because it's made obsolete by the second patch in this patchset:
> 
>    https://lore.kernel.org/linux-btrfs/cb12212b9c599817507f3978c9102767267625b2.1719825714.git.fdmanana@suse.com/
> 
> 5) There will be further improvements to the shrinker, namely to
>    reduce the latency of finding open inodes in a root, but those
>    will come later and may be too much for 6.10 final. It would also
>    require different patch versions for 6.10 and 6.11 (for-next) since
>    in the former we use a rbtree while in the later we have a xarray
>    now.
> 
> Thanks.
> 
> Filipe Manana (3):
>   btrfs: use delayed iput during extent map shrinking
>   btrfs: stop extent map shrinker if reschedule is needed
>   btrfs: avoid races when tracking progress for extent map shrinking

Thanks for the fixes, this seems to be urgent, I'd rather not delay
getting the fixes via stable with a 2 week delay. I'm going to send a
pull request for 6.10, the problems have been reported by early testing
users and will be most likely seen by more after release.

I hope this gives it enough justification despite the patch sizes and
ETA of 6.10 release.