On Mon, Jun 09, 2025 at 08:48:02AM -0700, Darrick J. Wong wrote:
> On Thu, Jun 05, 2025 at 01:33:52PM -0400, Brian Foster wrote:
> > Add a new filemap_get_folios_dirty() helper to look up existing dirty
> > folios in a range and add them to a folio_batch. This is to support
> > optimization of certain iomap operations that only care about dirty
> > folios in a target range. For example, zero range only zeroes the subset
> > of dirty pages over unwritten mappings, seek hole/data may use similar
> > logic in the future, etc.
> >
> > Note that the helper is intended for use under internal fs locks.
> > Therefore it trylocks folios in order to filter out clean folios.
> > This loosely follows the logic from filemap_range_has_writeback().
> >
> > Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
>
> You might want to cc willy directly on this one...
Er yeah, I'll do that for v2.
> > ---
> > include/linux/pagemap.h | 2 ++
> > mm/filemap.c | 42 +++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 44 insertions(+)
> >
...
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index bada249b9fb7..d28e984cdfd4 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2334,6 +2334,48 @@ unsigned filemap_get_folios_tag(struct address_space *mapping, pgoff_t *start,
> > }
> > EXPORT_SYMBOL(filemap_get_folios_tag);
> >
> > +unsigned filemap_get_folios_dirty(struct address_space *mapping, pgoff_t *start,
> > + pgoff_t end, struct folio_batch *fbatch)
>
> This ought to have a comment explaining what the function does.
> It identifies every folio starting at @*start and ending before @end
> that is dirty and tries to assign them to @fbatch, right?
>
Yep, or at least every folio that starts before end. I'll add a comment
and incorporate all the followup feedback. Thanks.
Brian
> The code looks reasonable to me; hopefully there aren't some subtleties
> that I'm missing here :P
>
> > +{
> > + XA_STATE(xas, &mapping->i_pages, *start);
> > + struct folio *folio;
> > +
> > + rcu_read_lock();
> > + while ((folio = find_get_entry(&xas, end, XA_PRESENT)) != NULL) {
> > + if (xa_is_value(folio))
> > + continue;
> > + if (folio_trylock(folio)) {
> > + bool clean = !folio_test_dirty(folio) &&
> > + !folio_test_writeback(folio);
> > + folio_unlock(folio);
> > + if (clean) {
> > + folio_put(folio);
> > + continue;
> > + }
> > + }
> > + if (!folio_batch_add(fbatch, folio)) {
> > + unsigned long nr = folio_nr_pages(folio);
> > + *start = folio->index + nr;
> > + goto out;
> > + }
> > + }
> > + /*
> > + * We come here when there is no page beyond @end. We take care to not
>
> ...no folio beyond @end?
>
> --D
>
> > + * overflow the index @start as it confuses some of the callers. This
> > + * breaks the iteration when there is a page at index -1 but that is
> > + * already broke anyway.
> > + */
> > + if (end == (pgoff_t)-1)
> > + *start = (pgoff_t)-1;
> > + else
> > + *start = end + 1;
> > +out:
> > + rcu_read_unlock();
> > +
> > + return folio_batch_count(fbatch);
> > +}
> > +EXPORT_SYMBOL(filemap_get_folios_dirty);
> > +
> > /*
> > * CD/DVDs are error prone. When a medium error occurs, the driver may fail
> > * a _large_ part of the i/o request. Imagine the worst scenario:
> > --
> > 2.49.0
> >
> >
>
