Re: [PATCH 00/13] btrfs: make read repair work in synchronous mode

[David Sterba <dsterba@suse.cz>]

On Tue, May 03, 2022 at 02:49:44PM +0800, Qu Wenruo wrote:
 
> By this we can:
> - Remove the re-entry behavior of endio function
>   Now everything is handled inside end_bio_extent_readpage().
> 
> - Remove the io_failure_tree completely
>   As we don't need to record which mirror has failed.
> 
> - Slightly reduced overhead on read repair
>   Now we won't call btrfs_map_bio() for each corrupted sector, as we can
>   merge the sectors into a much larger bio.

I thake this as the summary points for the whole patchset and frankly I
don't see it justified given all the new problems with the preallocation
and shuffling with the structures. What we have now is not perfect and I
would like to get rid of the io_failure_tree too, yet it works.

The main point is probably to stop reentering the functions, though the
idea of having a single tree that tracks the repair state and there are
callbacks dealing with that is not IMHO bad design. The alternative is
to complicate data structures and endio handler. I'm not sure if it's
worth the risk.