Re: [PATCH 2/5] ceph: Remove error return from ceph_process_folio_batch()

[Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>]

On Tue, 2025-12-30 at 18:43 -0800, Sam Edwards wrote:
> Following the previous patch, ceph_process_folio_batch() no longer
> returns errors because the writeback loop cannot handle them.

I am not completely convinced that we can remove returning error code here. What
if we don't process any folio in ceph_process_folio_batch(), then we cannot call
the ceph_submit_write(). It sounds to me that we need to have error code to jump
to release_folios in such case.

> 
> Since this function already indicates failure to lock any pages by
> leaving `ceph_wbc.locked_pages == 0`, and the writeback loop has no way

Frankly speaking, I don't quite follow what do you mean by "this function
already indicates failure to lock any pages". What do you mean here?

> to handle abandonment of a locked batch, change the return type of
> ceph_process_folio_batch() to `void` and remove the pathological goto in
> the writeback loop. The lack of a return code emphasizes that
> ceph_process_folio_batch() is designed to be abort-free: that is, once
> it commits a folio for writeback, it will not later abandon it or
> propagate an error for that folio.

I think you need to explain your point more clear. Currently, I am not convinced
that this modification makes sense.

Thanks,
Slava.

> 
> Signed-off-by: Sam Edwards <CFSworks@gmail.com>
> ---
>  fs/ceph/addr.c | 17 +++++------------
>  1 file changed, 5 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> index 3462df35d245..2b722916fb9b 100644
> --- a/fs/ceph/addr.c
> +++ b/fs/ceph/addr.c
> @@ -1283,16 +1283,16 @@ static inline int move_dirty_folio_in_page_array(struct address_space *mapping,
>  }
>  
>  static
> -int ceph_process_folio_batch(struct address_space *mapping,
> -			     struct writeback_control *wbc,
> -			     struct ceph_writeback_ctl *ceph_wbc)
> +void ceph_process_folio_batch(struct address_space *mapping,
> +			      struct writeback_control *wbc,
> +			      struct ceph_writeback_ctl *ceph_wbc)
>  {
>  	struct inode *inode = mapping->host;
>  	struct ceph_fs_client *fsc = ceph_inode_to_fs_client(inode);
>  	struct ceph_client *cl = fsc->client;
>  	struct folio *folio = NULL;
>  	unsigned i;
> -	int rc = 0;
> +	int rc;
>  
>  	for (i = 0; can_next_page_be_processed(ceph_wbc, i); i++) {
>  		folio = ceph_wbc->fbatch.folios[i];
> @@ -1322,12 +1322,10 @@ int ceph_process_folio_batch(struct address_space *mapping,
>  		rc = ceph_check_page_before_write(mapping, wbc,
>  						  ceph_wbc, folio);
>  		if (rc == -ENODATA) {
> -			rc = 0;
>  			folio_unlock(folio);
>  			ceph_wbc->fbatch.folios[i] = NULL;
>  			continue;
>  		} else if (rc == -E2BIG) {
> -			rc = 0;
>  			folio_unlock(folio);
>  			ceph_wbc->fbatch.folios[i] = NULL;
>  			break;
> @@ -1369,7 +1367,6 @@ int ceph_process_folio_batch(struct address_space *mapping,
>  		rc = move_dirty_folio_in_page_array(mapping, wbc, ceph_wbc,
>  				folio);
>  		if (rc) {
> -			rc = 0;
>  			folio_redirty_for_writepage(wbc, folio);
>  			folio_unlock(folio);
>  			break;
> @@ -1380,8 +1377,6 @@ int ceph_process_folio_batch(struct address_space *mapping,
>  	}
>  
>  	ceph_wbc->processed_in_fbatch = i;
> -
> -	return rc;
>  }
>  
>  static inline
> @@ -1685,10 +1680,8 @@ static int ceph_writepages_start(struct address_space *mapping,
>  			break;
>  
>  process_folio_batch:
> -		rc = ceph_process_folio_batch(mapping, wbc, &ceph_wbc);
> +		ceph_process_folio_batch(mapping, wbc, &ceph_wbc);
>  		ceph_shift_unused_folios_left(&ceph_wbc.fbatch);
> -		if (rc)
> -			goto release_folios;
>  
>  		/* did we get anything? */
>  		if (!ceph_wbc.locked_pages)