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Wong" Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org, hch@infradead.org, willy@infradead.org Subject: Re: [PATCH v3 3/7] iomap: optional zero range dirty folio processing Message-ID: References: <20250714204122.349582-1-bfoster@redhat.com> <20250714204122.349582-4-bfoster@redhat.com> <20250715052259.GO2672049@frogsfrogsfrogs> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250715052259.GO2672049@frogsfrogsfrogs> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 On Mon, Jul 14, 2025 at 10:22:59PM -0700, Darrick J. Wong wrote: > On Mon, Jul 14, 2025 at 04:41:18PM -0400, Brian Foster wrote: > > The only way zero range can currently process unwritten mappings > > with dirty pagecache is to check whether the range is dirty before > > mapping lookup and then flush when at least one underlying mapping > > is unwritten. This ordering is required to prevent iomap lookup from > > racing with folio writeback and reclaim. > > > > Since zero range can skip ranges of unwritten mappings that are > > clean in cache, this operation can be improved by allowing the > > filesystem to provide a set of dirty folios that require zeroing. In > > turn, rather than flush or iterate file offsets, zero range can > > iterate on folios in the batch and advance over clean or uncached > > ranges in between. > > > > Add a folio_batch in struct iomap and provide a helper for fs' to > > /me confused by the single quote; is this supposed to read: > > "...for the fs to populate..."? > Eh, I intended it to read "for filesystems to populate." I'll change it to that locally. Brian > Either way the code changes look like a reasonable thing to do for the > pagecache (try to grab a bunch of dirty folios while XFS holds the > mapping lock) so > > Reviewed-by: "Darrick J. Wong" > > --D > > > > populate the batch at lookup time. Update the folio lookup path to > > return the next folio in the batch, if provided, and advance the > > iter if the folio starts beyond the current offset. > > > > Signed-off-by: Brian Foster > > Reviewed-by: Christoph Hellwig > > --- > > fs/iomap/buffered-io.c | 89 +++++++++++++++++++++++++++++++++++++++--- > > fs/iomap/iter.c | 6 +++ > > include/linux/iomap.h | 4 ++ > > 3 files changed, 94 insertions(+), 5 deletions(-) > > > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > > index 38da2fa6e6b0..194e3cc0857f 100644 > > --- a/fs/iomap/buffered-io.c > > +++ b/fs/iomap/buffered-io.c > > @@ -750,6 +750,28 @@ static struct folio *__iomap_get_folio(struct iomap_iter *iter, size_t len) > > if (!mapping_large_folio_support(iter->inode->i_mapping)) > > len = min_t(size_t, len, PAGE_SIZE - offset_in_page(pos)); > > > > + if (iter->fbatch) { > > + struct folio *folio = folio_batch_next(iter->fbatch); > > + > > + if (!folio) > > + return NULL; > > + > > + /* > > + * The folio mapping generally shouldn't have changed based on > > + * fs locks, but be consistent with filemap lookup and retry > > + * the iter if it does. > > + */ > > + folio_lock(folio); > > + if (unlikely(folio->mapping != iter->inode->i_mapping)) { > > + iter->iomap.flags |= IOMAP_F_STALE; > > + folio_unlock(folio); > > + return NULL; > > + } > > + > > + folio_get(folio); > > + return folio; > > + } > > + > > if (folio_ops && folio_ops->get_folio) > > return folio_ops->get_folio(iter, pos, len); > > else > > @@ -811,6 +833,8 @@ static int iomap_write_begin(struct iomap_iter *iter, struct folio **foliop, > > int status = 0; > > > > len = min_not_zero(len, *plen); > > + *foliop = NULL; > > + *plen = 0; > > > > if (fatal_signal_pending(current)) > > return -EINTR; > > @@ -819,6 +843,15 @@ static int iomap_write_begin(struct iomap_iter *iter, struct folio **foliop, > > if (IS_ERR(folio)) > > return PTR_ERR(folio); > > > > + /* > > + * No folio means we're done with a batch. We still have range to > > + * process so return and let the caller iterate and refill the batch. > > + */ > > + if (!folio) { > > + WARN_ON_ONCE(!iter->fbatch); > > + return 0; > > + } > > + > > /* > > * Now we have a locked folio, before we do anything with it we need to > > * check that the iomap we have cached is not stale. The inode extent > > @@ -839,6 +872,21 @@ static int iomap_write_begin(struct iomap_iter *iter, struct folio **foliop, > > } > > } > > > > + /* > > + * The folios in a batch may not be contiguous. If we've skipped > > + * forward, advance the iter to the pos of the current folio. If the > > + * folio starts beyond the end of the mapping, it may have been trimmed > > + * since the lookup for whatever reason. Return a NULL folio to > > + * terminate the op. > > + */ > > + if (folio_pos(folio) > iter->pos) { > > + len = min_t(u64, folio_pos(folio) - iter->pos, > > + iomap_length(iter)); > > + status = iomap_iter_advance(iter, &len); > > + if (status || !len) > > + goto out_unlock; > > + } > > + > > pos = iomap_trim_folio_range(iter, folio, poffset, &len); > > > > if (srcmap->type == IOMAP_INLINE) > > @@ -1377,6 +1425,12 @@ static int iomap_zero_iter(struct iomap_iter *iter, bool *did_zero) > > if (iter->iomap.flags & IOMAP_F_STALE) > > break; > > > > + /* a NULL folio means we're done with a folio batch */ > > + if (!folio) { > > + status = iomap_iter_advance_full(iter); > > + break; > > + } > > + > > /* warn about zeroing folios beyond eof that won't write back */ > > WARN_ON_ONCE(folio_pos(folio) > iter->inode->i_size); > > > > @@ -1398,6 +1452,26 @@ static int iomap_zero_iter(struct iomap_iter *iter, bool *did_zero) > > return status; > > } > > > > +loff_t > > +iomap_fill_dirty_folios( > > + struct iomap_iter *iter, > > + loff_t offset, > > + loff_t length) > > +{ > > + struct address_space *mapping = iter->inode->i_mapping; > > + pgoff_t start = offset >> PAGE_SHIFT; > > + pgoff_t end = (offset + length - 1) >> PAGE_SHIFT; > > + > > + iter->fbatch = kmalloc(sizeof(struct folio_batch), GFP_KERNEL); > > + if (!iter->fbatch) > > + return offset + length; > > + folio_batch_init(iter->fbatch); > > + > > + filemap_get_folios_dirty(mapping, &start, end, iter->fbatch); > > + return (start << PAGE_SHIFT); > > +} > > +EXPORT_SYMBOL_GPL(iomap_fill_dirty_folios); > > + > > int > > iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero, > > const struct iomap_ops *ops, void *private) > > @@ -1426,7 +1500,7 @@ iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero, > > * flushing on partial eof zeroing, special case it to zero the > > * unaligned start portion if already dirty in pagecache. > > */ > > - if (off && > > + if (!iter.fbatch && off && > > filemap_range_needs_writeback(mapping, pos, pos + plen - 1)) { > > iter.len = plen; > > while ((ret = iomap_iter(&iter, ops)) > 0) > > @@ -1442,13 +1516,18 @@ iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero, > > * if dirty and the fs returns a mapping that might convert on > > * writeback. > > */ > > - range_dirty = filemap_range_needs_writeback(inode->i_mapping, > > - iter.pos, iter.pos + iter.len - 1); > > + range_dirty = filemap_range_needs_writeback(mapping, iter.pos, > > + iter.pos + iter.len - 1); > > while ((ret = iomap_iter(&iter, ops)) > 0) { > > const struct iomap *srcmap = iomap_iter_srcmap(&iter); > > > > - if (srcmap->type == IOMAP_HOLE || > > - srcmap->type == IOMAP_UNWRITTEN) { > > + if (WARN_ON_ONCE(iter.fbatch && > > + srcmap->type != IOMAP_UNWRITTEN)) > > + return -EIO; > > + > > + if (!iter.fbatch && > > + (srcmap->type == IOMAP_HOLE || > > + srcmap->type == IOMAP_UNWRITTEN)) { > > s64 status; > > > > if (range_dirty) { > > diff --git a/fs/iomap/iter.c b/fs/iomap/iter.c > > index 6ffc6a7b9ba5..89bd5951a6fd 100644 > > --- a/fs/iomap/iter.c > > +++ b/fs/iomap/iter.c > > @@ -9,6 +9,12 @@ > > > > static inline void iomap_iter_reset_iomap(struct iomap_iter *iter) > > { > > + if (iter->fbatch) { > > + folio_batch_release(iter->fbatch); > > + kfree(iter->fbatch); > > + iter->fbatch = NULL; > > + } > > + > > iter->status = 0; > > memset(&iter->iomap, 0, sizeof(iter->iomap)); > > memset(&iter->srcmap, 0, sizeof(iter->srcmap)); > > diff --git a/include/linux/iomap.h b/include/linux/iomap.h > > index 522644d62f30..0b9b460b2873 100644 > > --- a/include/linux/iomap.h > > +++ b/include/linux/iomap.h > > @@ -9,6 +9,7 @@ > > #include > > #include > > #include > > +#include > > > > struct address_space; > > struct fiemap_extent_info; > > @@ -239,6 +240,7 @@ struct iomap_iter { > > unsigned flags; > > struct iomap iomap; > > struct iomap srcmap; > > + struct folio_batch *fbatch; > > void *private; > > }; > > > > @@ -345,6 +347,8 @@ void iomap_invalidate_folio(struct folio *folio, size_t offset, size_t len); > > bool iomap_dirty_folio(struct address_space *mapping, struct folio *folio); > > int iomap_file_unshare(struct inode *inode, loff_t pos, loff_t len, > > const struct iomap_ops *ops); > > +loff_t iomap_fill_dirty_folios(struct iomap_iter *iter, loff_t offset, > > + loff_t length); > > int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, > > bool *did_zero, const struct iomap_ops *ops, void *private); > > int iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero, > > -- > > 2.50.0 > > > > >