On Fri, Nov 08, 2024 at 07:01:27PM -0800, Darrick J. Wong wrote:
> On Fri, Nov 08, 2024 at 07:42:44AM -0500, Brian Foster wrote:
> > In preparation for special handling of subranges, lift the zeroed
> > mapping logic from the iterator into the caller. Since this puts the
> > pagecache dirty check and flushing in the same place, streamline the
> > comments a bit as well.
> >
> > Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
> > ---
> > fs/iomap/buffered-io.c | 64 +++++++++++++++---------------------------
> > 1 file changed, 22 insertions(+), 42 deletions(-)
> >
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index ef0b68bccbb6..a78b5b9b3df3 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -1350,40 +1350,12 @@ static inline int iomap_zero_iter_flush_and_stale(struct iomap_iter *i)
> > return filemap_write_and_wait_range(mapping, i->pos, end);
> > }
> >
> > -static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero,
> > - bool *range_dirty)
> > +static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
> > {
> > - const struct iomap *srcmap = iomap_iter_srcmap(iter);
> > loff_t pos = iter->pos;
> > loff_t length = iomap_length(iter);
> > loff_t written = 0;
> >
> > - /*
> > - * We must zero subranges of unwritten mappings that might be dirty in
> > - * pagecache from previous writes. We only know whether the entire range
> > - * was clean or not, however, and dirty folios may have been written
> > - * back or reclaimed at any point after mapping lookup.
> > - *
> > - * The easiest way to deal with this is to flush pagecache to trigger
> > - * any pending unwritten conversions and then grab the updated extents
> > - * from the fs. The flush may change the current mapping, so mark it
> > - * stale for the iterator to remap it for the next pass to handle
> > - * properly.
> > - *
> > - * Note that holes are treated the same as unwritten because zero range
> > - * is (ab)used for partial folio zeroing in some cases. Hole backed
> > - * post-eof ranges can be dirtied via mapped write and the flush
> > - * triggers writeback time post-eof zeroing.
> > - */
> > - if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN) {
> > - if (*range_dirty) {
> > - *range_dirty = false;
> > - return iomap_zero_iter_flush_and_stale(iter);
> > - }
> > - /* range is clean and already zeroed, nothing to do */
> > - return length;
> > - }
> > -
> > do {
> > struct folio *folio;
> > int status;
> > @@ -1433,24 +1405,32 @@ iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
> > bool range_dirty;
> >
> > /*
> > - * Zero range wants to skip pre-zeroed (i.e. unwritten) mappings, but
> > - * pagecache must be flushed to ensure stale data from previous
> > - * buffered writes is not exposed. A flush is only required for certain
> > - * types of mappings, but checking pagecache after mapping lookup is
> > - * racy with writeback and reclaim.
> > + * Zero range can skip mappings that are zero on disk so long as
> > + * pagecache is clean. If pagecache was dirty prior to zero range, the
> > + * mapping converts on writeback completion and so must be zeroed.
> > *
> > - * Therefore, check the entire range first and pass along whether any
> > - * part of it is dirty. If so and an underlying mapping warrants it,
> > - * flush the cache at that point. This trades off the occasional false
> > - * positive (and spurious flush, if the dirty data and mapping don't
> > - * happen to overlap) for simplicity in handling a relatively uncommon
> > - * situation.
> > + * The simplest way to deal with this across a range is to flush
> > + * pagecache and process the updated mappings. To avoid an unconditional
> > + * flush, check pagecache state and only flush if dirty and the fs
> > + * returns a mapping that might convert on writeback.
> > */
> > range_dirty = filemap_range_needs_writeback(inode->i_mapping,
> > pos, pos + len - 1);
> > + while ((ret = iomap_iter(&iter, ops)) > 0) {
> > + const struct iomap *s = iomap_iter_srcmap(&iter);
> > +
> > + if (s->type == IOMAP_HOLE || s->type == IOMAP_UNWRITTEN) {
> > + loff_t p = iomap_length(&iter);
>
> Another dumb nit: blank line after the declaration.
>
Fixed.
> With that fixed, this is ok by me for further testing:
> Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
>
Thanks.
Brian
> --D
>
> > + if (range_dirty) {
> > + range_dirty = false;
> > + p = iomap_zero_iter_flush_and_stale(&iter);
> > + }
> > + iter.processed = p;
> > + continue;
> > + }
> >
> > - while ((ret = iomap_iter(&iter, ops)) > 0)
> > - iter.processed = iomap_zero_iter(&iter, did_zero, &range_dirty);
> > + iter.processed = iomap_zero_iter(&iter, did_zero);
> > + }
> > return ret;
> > }
> > EXPORT_SYMBOL_GPL(iomap_zero_range);
> > --
> > 2.47.0
> >
> >
>
