On Mon, Jun 9, 2025 at 9:38 AM Darrick J. Wong <djwong@xxxxxxxxxx> wrote:
>
> On Fri, Jun 06, 2025 at 04:37:58PM -0700, Joanne Koong wrote:
> > Add buffered write support for IOMAP_IN_MEM iomaps. This lets
> > IOMAP_IN_MEM iomaps use some of the internal features in iomaps
> > such as granular dirty tracking for large folios.
> >
> > Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> > ---
> > fs/iomap/buffered-io.c | 24 +++++++++++++++++-------
> > include/linux/iomap.h | 10 ++++++++++
> > 2 files changed, 27 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index 1caeb4921035..fd2ea1306d88 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -300,7 +300,7 @@ static inline bool iomap_block_needs_zeroing(const struct iomap_iter *iter,
> > {
> > const struct iomap *srcmap = iomap_iter_srcmap(iter);
> >
> > - return srcmap->type != IOMAP_MAPPED ||
> > + return (srcmap->type != IOMAP_MAPPED && srcmap->type != IOMAP_IN_MEM) ||
> > (srcmap->flags & IOMAP_F_NEW) ||
> > pos >= i_size_read(iter->inode);
> > }
> > @@ -583,16 +583,26 @@ iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
> > pos + len - 1);
> > }
> >
> > -static int iomap_read_folio_sync(loff_t block_start, struct folio *folio,
> > - size_t poff, size_t plen, const struct iomap *iomap)
> > +static int iomap_read_folio_sync(const struct iomap_iter *iter, loff_t block_start,
> > + struct folio *folio, size_t poff, size_t plen)
> > {
> > - return iomap_bio_read_folio_sync(block_start, folio, poff, plen, iomap);
> > + const struct iomap_folio_ops *folio_ops = iter->iomap.folio_ops;
> > + const struct iomap *srcmap = iomap_iter_srcmap(iter);
> > +
> > + if (folio_ops && folio_ops->read_folio_sync)
> > + return folio_ops->read_folio_sync(block_start, folio,
> > + poff, plen, srcmap,
> > + iter->private);
>
> Hmm, patch 6 hooks this up to fuse_do_readfolio, which means that iomap
> provides the folios and manages their uptodate/dirty state. You still
> want fuse to handle the folio contents (aka poke the fuse server via
> FUSE_READ/FUSE_WRITE), but this avoids the memcpy that IOMAP_INLINE
> performs.
>
> So I think you're effectively addding another IO path to buffered-io.c,
> which explains why you moved the bio code to a separate file. I wonder
The bio code needed to be moved to its own separate file because it
depends on CONFIG_BLOCK whereas fuse should still compile/run even if
CONFIG_BLOCK is not set.
Btw, I think you will need this too for your fuse server iomap patchset.
> if you could hook up this new IO path by checking for a non-NULL
> ->read_folio_sync function and calling it regardless of iomap::type?
I think this is already doing that? It will call ->read_folio_sync()
if the callback was provided, regardless of what the iomap type is.
>
> --D
>
> > +
> > + /* IOMAP_IN_MEM iomaps must always handle ->read_folio_sync() */
> > + WARN_ON_ONCE(iter->iomap.type == IOMAP_IN_MEM);
> > +
> > + return iomap_bio_read_folio_sync(block_start, folio, poff, plen, srcmap);
> > }
> >
> > static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
> > size_t len, struct folio *folio)
> > {
> > - const struct iomap *srcmap = iomap_iter_srcmap(iter);
> > struct iomap_folio_state *ifs;
> > loff_t block_size = i_blocksize(iter->inode);
> > loff_t block_start = round_down(pos, block_size);
> > @@ -640,8 +650,8 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
> > if (iter->flags & IOMAP_NOWAIT)
> > return -EAGAIN;
> >
> > - status = iomap_read_folio_sync(block_start, folio,
> > - poff, plen, srcmap);
> > + status = iomap_read_folio_sync(iter, block_start, folio,
> > + poff, plen);
> > if (status)
> > return status;
> > }
> > diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> > index dbbf217eb03f..e748aeebe1a5 100644
> > --- a/include/linux/iomap.h
> > +++ b/include/linux/iomap.h
> > @@ -175,6 +175,16 @@ struct iomap_folio_ops {
> > * locked by the iomap code.
> > */
> > bool (*iomap_valid)(struct inode *inode, const struct iomap *iomap);
> > +
> > + /*
> > + * Required for IOMAP_IN_MEM iomaps. Otherwise optional if the caller
> > + * wishes to handle reading in a folio.
> > + *
> > + * The read must be done synchronously.
> > + */
> > + int (*read_folio_sync)(loff_t block_start, struct folio *folio,
> > + size_t off, size_t len, const struct iomap *iomap,
> > + void *private);
> > };
> >
> > /*
> > --
> > 2.47.1
> >
> >
