Re: [PATCH 05/11] btrfs: remove bioc->stripes_pending

[Nikolay Borisov <nborisov@suse.com>]

On 13.07.22 г. 9:13 ч., Christoph Hellwig wrote:
> The stripes_pending in the btrfs_io_context counts number of inflight
> low-level bios for an upper btrfs_bio.  For reads this is generally
> one as reads are never cloned, while for writes we can trivially use
> the bio remaining mechanisms that is used for chained bios.
> 
> To be able to make use of that mechanism, split out a separate trivial
> end_io handler for the cloned bios that does a minimal amount of error
> tracking and which then calls bio_endio on the original bio to transfer
> control to that, with the remaining counter making sure it is completed
> last.  This then allows to merge btrfs_end_bioc into the original bio
> bi_end_io handler.  To make this all work all error handling needs to
> happen through the bi_end_io handler, which requires a small amount
> of reshuffling in submit_stripe_bio so that the bio is cloned already
> by the time the suitability of the device is checked.
> 
> This reduces the size of the btrfs_io_context and prepares splitting
> the btrfs_bio at the stripe boundary.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>