On Tue, Jul 15, 2025 at 08:35:51AM -0400, Brian Foster wrote:
> On Mon, Jul 14, 2025 at 10:28:11PM -0700, Darrick J. Wong wrote:
> > On Mon, Jul 14, 2025 at 04:41:20PM -0400, Brian Foster wrote:
> > > Use the iomap folio batch mechanism to select folios to zero on zero
> > > range of unwritten mappings. Trim the resulting mapping if the batch
> > > is filled (unlikely for current use cases) to distinguish between a
> > > range to skip and one that requires another iteration due to a full
> > > batch.
> > >
> > > Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
> > > Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> > > ---
> > > fs/xfs/xfs_iomap.c | 23 +++++++++++++++++++++++
> > > 1 file changed, 23 insertions(+)
> > >
> > > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> > > index b5cf5bc6308d..63054f7ead0e 100644
> > > --- a/fs/xfs/xfs_iomap.c
> > > +++ b/fs/xfs/xfs_iomap.c
> > > @@ -1691,6 +1691,8 @@ xfs_buffered_write_iomap_begin(
> > > struct iomap *iomap,
> > > struct iomap *srcmap)
> > > {
> > > + struct iomap_iter *iter = container_of(iomap, struct iomap_iter,
> > > + iomap);
> > > struct xfs_inode *ip = XFS_I(inode);
> > > struct xfs_mount *mp = ip->i_mount;
> > > xfs_fileoff_t offset_fsb = XFS_B_TO_FSBT(mp, offset);
> > > @@ -1762,6 +1764,7 @@ xfs_buffered_write_iomap_begin(
> > > */
> > > if (flags & IOMAP_ZERO) {
> > > xfs_fileoff_t eof_fsb = XFS_B_TO_FSB(mp, XFS_ISIZE(ip));
> > > + u64 end;
> > >
> > > if (isnullstartblock(imap.br_startblock) &&
> > > offset_fsb >= eof_fsb)
> > > @@ -1769,6 +1772,26 @@ xfs_buffered_write_iomap_begin(
> > > if (offset_fsb < eof_fsb && end_fsb > eof_fsb)
> > > end_fsb = eof_fsb;
> > >
> > > + /*
> > > + * Look up dirty folios for unwritten mappings within EOF.
> > > + * Providing this bypasses the flush iomap uses to trigger
> > > + * extent conversion when unwritten mappings have dirty
> > > + * pagecache in need of zeroing.
> > > + *
> > > + * Trim the mapping to the end pos of the lookup, which in turn
> > > + * was trimmed to the end of the batch if it became full before
> > > + * the end of the mapping.
> > > + */
> > > + if (imap.br_state == XFS_EXT_UNWRITTEN &&
> > > + offset_fsb < eof_fsb) {
> > > + loff_t len = min(count,
> > > + XFS_FSB_TO_B(mp, imap.br_blockcount));
> > > +
> > > + end = iomap_fill_dirty_folios(iter, offset, len);
> > > + end_fsb = min_t(xfs_fileoff_t, end_fsb,
> > > + XFS_B_TO_FSB(mp, end));
> >
> > Hrmm. XFS_B_TO_FSB and not _FSBT? Can the rounding up behavior result
> > in a missed byte range? I think the answer is no because @end should be
> > aligned to a folio boundary, and folios can't be smaller than an
> > fsblock.
> >
>
> Hmm.. not that I'm aware of..? Please elaborate if there's a case you're
> suspicious of because I could have certainly got my wires crossed.
I don't have a specific case in mind. I saw the conversion function and
thought "well, what IF the return value from iomap_fill_dirty_folios
isn't aligned to a fsblock?" and then went around trying to prove that
isn't possible. :)
> My thinking is that end_fsb reflects the first fsb beyond the target
> range. I.e., it's calculated and used as such in xfs_iomap_end_fsb() and
> the various xfs_trim_extent() calls throughout the rest of the function.
<nod> So I think we're fine here.
--D
> Brian
>
> > If the answer to the second question is indeed "no" then I think this is
> > ok and
> > Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
> >
> > --D
> >
> >
> > > + }
> > > +
> > > xfs_trim_extent(&imap, offset_fsb, end_fsb - offset_fsb);
> > > }
> > >
> > > --
> > > 2.50.0
> > >
> > >
> >
>
>
