Re: [PATCH v3 1/2] f2fs: complete dropbehind write bios in safe task context

[Wenjie Qi]

  Thanks, I missed that these helpers had landed for 7.3.

  I'll rebase the next revision and use BIO_COMPLETE_IN_TASK for dropbehind
  write bios, removing the F2FS-local context check and dropbehind-specific
  workqueue deferral. I'll also Cc the people and lists involved with the
  common code.

On Tue, Aug 25, 2026 at 1:48 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> On Mon, Aug 24, 2026 at 06:33:46PM +0800, Wenjie Qi wrote:
> > Buffered RWF_DONTCACHE writes invalidate dropbehind folios from writeback
> > completion. Keep normal and dropbehind folios in separate write bios, and
> > defer dropbehind bios to sbi->wq unless completion runs in preemptible task
> > context.
> >
> > Use an F2FS-local context check for this decision. Task context alone is
> > not sufficient: preemption may still be disabled, or completion may run in
> > a preemptible RCU read-side critical section.
> >
> > Keep the existing large-ATC deferral unchanged.
>
> Please reuse all the helpers added in common code in 7.3 for deferring
> bios and tsting if that that is neeeded instead of badly reinventing
> the logic.  It also is really helpful to Cc people involved with the
> code and the relevant mailing lists.
>
> >
> > Signed-off-by: Wenjie Qi <qiwenjie@xxxxxxxxxx>
> > ---
> >  fs/f2fs/data.c | 50 ++++++++++++++++++++++++++++++++++++++++++--------
> >  1 file changed, 42 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index 6ae0eb37d20..774a3e2d8e3 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -21,6 +21,7 @@
> >  #include <linux/fiemap.h>
> >  #include <linux/iomap.h>
> >  #include <linux/fserror.h>
> > +#include <linux/rcupdate.h>
> >
> >  #include "f2fs.h"
> >  #include "node.h"
> > @@ -43,9 +44,29 @@ struct f2fs_folio_state {
> >
> >  struct f2fs_bio {
> >       struct work_struct work;
> > +     bool dropbehind;
> >       struct bio bio;
> >  };
> >
> > +static struct f2fs_bio *to_f2fs_bio(struct bio *bio)
> > +{
> > +     return container_of(bio, struct f2fs_bio, bio);
> > +}
> > +
> > +/* Keep in sync with the proposed block-layer bio_in_atomic(). */
> > +static bool f2fs_bio_in_atomic(void)
> > +{
> > +#ifdef CONFIG_PREEMPTION
> > +     if (rcu_preempt_depth())
> > +             return true;
> > +#endif
> > +#ifndef CONFIG_PREEMPT_COUNT
> > +     return true;
> > +#else
> > +     return !preemptible();
> > +#endif
> > +}
> > +
> >  #define      F2FS_BIO_POOL_SIZE      NR_CURSEG_TYPE
> >
> >  int __init f2fs_init_bioset(void)
> > @@ -426,12 +447,13 @@ static void f2fs_write_end_io(struct bio *bio)
> >
> >       sbi = bio->bi_private;
> >
> > -     if (in_atomic() && bio->bi_iter.bi_size > sbi->max_atc_write_bio_size) {
> > -             struct work_struct *w;
> > +     if ((to_f2fs_bio(bio)->dropbehind && f2fs_bio_in_atomic()) ||
> > +         (in_atomic() &&
> > +          bio->bi_iter.bi_size > sbi->max_atc_write_bio_size)) {
> > +             struct work_struct *work = &to_f2fs_bio(bio)->work;
> >
> > -             w = &container_of(bio, struct f2fs_bio, bio)->work;
> > -             INIT_WORK(w, f2fs_write_end_io_work);
> > -             queue_work(sbi->wq, w);
> > +             INIT_WORK(work, f2fs_write_end_io_work);
> > +             queue_work(sbi->wq, work);
> >       } else {
> >               f2fs_write_end_bio(bio);
> >       }
> > @@ -530,6 +552,8 @@ static struct bio *__bio_alloc(struct f2fs_io_info *fio, int npages)
> >       bio = bio_alloc_bioset(bdev, npages,
> >                               fio->op | fio->op_flags | f2fs_io_flags(fio),
> >                               GFP_NOIO, &f2fs_bioset);
> > +     to_f2fs_bio(bio)->dropbehind =
> > +                     !is_read_io(fio->op) && folio_test_dropbehind(fio->folio);
> >       bio->bi_iter.bi_sector = sector;
> >       if (is_read_io(fio->op)) {
> >               bio->bi_end_io = f2fs_read_end_io;
> > @@ -825,6 +849,13 @@ static bool page_is_mergeable(struct f2fs_sb_info *sbi, struct bio *bio,
> >       return bio->bi_bdev == f2fs_target_device(sbi, cur_blkaddr, NULL);
> >  }
> >
> > +static bool f2fs_bio_dropbehind_mergeable(struct bio *bio,
> > +                                       struct f2fs_io_info *fio)
> > +{
> > +     return to_f2fs_bio(bio)->dropbehind ==
> > +             folio_test_dropbehind(fio->folio);
> > +}
> > +
> >  static bool io_type_is_mergeable(struct f2fs_bio_info *io,
> >                                               struct f2fs_io_info *fio)
> >  {
> > @@ -1017,8 +1048,10 @@ int f2fs_merge_page_bio(struct f2fs_io_info *fio)
> >
> >       trace_f2fs_submit_folio_bio(data_folio, fio);
> >
> > -     if (bio && !page_is_mergeable(fio->sbi, bio, *fio->last_block,
> > -                                             fio->new_blkaddr))
> > +     if (bio &&
> > +         (!page_is_mergeable(fio->sbi, bio, *fio->last_block,
> > +                             fio->new_blkaddr) ||
> > +          !f2fs_bio_dropbehind_mergeable(bio, fio)))
> >               f2fs_submit_merged_ipu_write(fio->sbi, &bio, NULL);
> >  alloc_new:
> >       if (!bio) {
> > @@ -1118,7 +1151,8 @@ void f2fs_submit_page_write(struct f2fs_io_info *fio)
> >           (!io_is_mergeable(sbi, io->bio, io, fio, io->last_block_in_bio,
> >                             fio->new_blkaddr) ||
> >            !f2fs_crypt_mergeable_bio(io->bio, fio_inode(fio),
> > -                             bio_folio->index, fio)))
> > +                             bio_folio->index, fio) ||
> > +          !f2fs_bio_dropbehind_mergeable(io->bio, fio)))
> >               __submit_merged_bio(io);
> >  alloc_new:
> >       if (io->bio == NULL) {
> > --
> > 2.43.0
> >
> ---end quoted text---