linux-kernel - Re: [PATCH v3 3/4] ceph: remove error return from ceph_process_folio

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Message-ID: <CAH5Ym4gTE_ueXXuDngBHWdUd=LU0SFQEB20vs0rSYL_BB4O-Tw@mail.gmail.com>
Date: Wed, 28 Jan 2026 16:29:53 -0800
From: Sam Edwards <cfsworks@...il.com>
To: Viacheslav Dubeyko <Slava.Dubeyko@....com>
Cc: Xiubo Li <xiubli@...hat.com>, "idryomov@...il.com" <idryomov@...il.com>, 
	Milind Changire <mchangir@...hat.com>, 
	"ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>, "brauner@...nel.org" <brauner@...nel.org>, 
	"jlayton@...nel.org" <jlayton@...nel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/4] ceph: remove error return from ceph_process_folio_batch()

On Mon, Jan 26, 2026 at 2:55 PM Viacheslav Dubeyko
<Slava.Dubeyko@....com> wrote:
>
> On Sun, 2026-01-25 at 18:30 -0800, Sam Edwards wrote:
> > Following an earlier commit, ceph_process_folio_batch() no longer
> > returns errors because the writeback loop cannot handle them.
> >
> > Since this function already indicates failure to lock any pages by
> > leaving `ceph_wbc.locked_pages == 0`, and the writeback loop has no way
> > 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. Any future changes requiring "abort"
> > logic should follow this invariant by cleaning up its array and
> > resetting ceph_wbc.locked_pages appropriately.
> >
> > Signed-off-by: Sam Edwards <CFSworks@...il.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 39064893f35b..cdf11288d6b7 100644
> > --- a/fs/ceph/addr.c
> > +++ b/fs/ceph/addr.c
> > @@ -1284,16 +1284,16 @@ 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)
>
> I still prefer to return the error code from the function.

Hi Slava,

Since the objection to this patch is mere preference at this point, we
need to seek broader consensus before either of us unilaterally
decides whether this style is appropriate for the CephFS subsystem.
I'm willing to follow the preferences of the group, we just need a
"group" first. :)

Christian: Since you committed the patch introducing the
ceph_process_folio_batch() function, would you like to weigh in?

Thanks,
Sam

>
> Thanks,
> Slava.
>
> > +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];
> > @@ -1323,12 +1323,10 @@ 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;
> > @@ -1370,7 +1368,6 @@ 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;
> > @@ -1381,8 +1378,6 @@ int ceph_process_folio_batch(struct address_space *mapping,
> >       }
> >
> >       ceph_wbc->processed_in_fbatch = i;
> > -
> > -     return rc;
> >  }
> >
> >  static inline
> > @@ -1686,10 +1681,8 @@ 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)