On Fri, Jul 11, 2025 at 9:41 PM Darrick J. Wong <djwong@xxxxxxxxxx> wrote:
>
> On Wed, Jul 09, 2025 at 03:10:20PM -0700, Joanne Koong wrote:
> > Use iomap for dirty folio writeback in ->writepages().
> > This allows for granular dirty writeback of large folios.
> >
> > Only the dirty portions of the large folio will be written instead of
> > having to write out the entire folio. For example if there is a 1 MB
> > large folio and only 2 bytes in it are dirty, only the page for those
> > dirty bytes will be written out.
> >
> > .dirty_folio needs to be set to iomap_dirty_folio so that the bitmap
> > iomap uses for dirty tracking correctly reflects dirty regions that need
> > to be written back.
> >
> > Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> > ---
> > fs/fuse/file.c | 127 +++++++++++++++++++++++++++++--------------------
> > 1 file changed, 76 insertions(+), 51 deletions(-)
> >
> > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > index cadad61ef7df..70bbc8f26459 100644
> > --- a/fs/fuse/file.c
> > +++ b/fs/fuse/file.c
> > @@ -2100,7 +2101,7 @@ struct fuse_fill_wb_data {
> > struct fuse_file *ff;
> > struct inode *inode;
> > unsigned int max_folios;
> > - unsigned int nr_pages;
> > + unsigned int nr_bytes;
>
> I don't know if fuse servers are ever realistically going to end up with
> a large number of 1M folios, but at least in theory iomap is capable of
> queuing ~4096 folios into a single writeback context. Does this need to
> account for that?
In fuse_writepage_need_send(), the writeback request gets sent out if
max pages can be exceeded (eg if ((data->nr_bytes + len) / PAGE_SIZE >
fc->max_pages)). max pages has a limit of 65535, which gives a limit
in bytes of 256 MB (eg 65535 * PAGE_SIZE), so I think having unsigned
int here for nr_bytes is okay.
>
> > };
> >
> > static bool fuse_pages_realloc(struct fuse_fill_wb_data *data)
> > @@ -2141,22 +2142,29 @@ static void fuse_writepages_send(struct fuse_fill_wb_data *data)
> > spin_unlock(&fi->lock);
> > }
> >
> > -static bool fuse_writepage_need_send(struct fuse_conn *fc, struct folio *folio,
> > - struct fuse_args_pages *ap,
> > +static bool fuse_writepage_need_send(struct fuse_conn *fc, loff_t pos,
> > + unsigned len, struct fuse_args_pages *ap,
> > struct fuse_fill_wb_data *data)
> > {
> > + struct folio *prev_folio;
> > + struct fuse_folio_desc prev_desc;
> > + loff_t prev_pos;
> > +
> > WARN_ON(!ap->num_folios);
> >
> > /* Reached max pages */
> > - if (data->nr_pages + folio_nr_pages(folio) > fc->max_pages)
> > + if ((data->nr_bytes + len) / PAGE_SIZE > fc->max_pages)
>
> >> PAGE_SHIFT ?
Nice, i'll change this to >> PAGE_SHIFT. Thanks for looking through
the patchset.
>
> Otherwise this looks decent to me.
>
> --D
>
> > return true;
