On Tue, Feb 27, 2024 at 11:06:37AM +0100, Pankaj Raghav (Samsung) wrote:
> On Mon, Feb 26, 2024 at 02:40:42PM +0000, Matthew Wilcox wrote:
> > On Mon, Feb 26, 2024 at 10:49:26AM +0100, Pankaj Raghav (Samsung) wrote:
> > > From: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> > >
> > > Supporting mapping_min_order implies that we guarantee each folio in the
> > > page cache has at least an order of mapping_min_order. So when adding new
> > > folios to the page cache we must ensure the index used is aligned to the
> > > mapping_min_order as the page cache requires the index to be aligned to
> > > the order of the folio.
> >
> > This seems like a remarkably complicated way of achieving:
> >
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 5603ced05fb7..36105dad4440 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2427,9 +2427,11 @@ static int filemap_update_page(struct kiocb *iocb,
> > }
> >
> > static int filemap_create_folio(struct file *file,
> > - struct address_space *mapping, pgoff_t index,
> > + struct address_space *mapping, loff_t pos,
> > struct folio_batch *fbatch)
> > {
> > + pgoff_t index;
> > + unsigned int min_order;
> > struct folio *folio;
> > int error;
> >
> > @@ -2451,6 +2453,8 @@ static int filemap_create_folio(struct file *file,
> > * well to keep locking rules simple.
> > */
> > filemap_invalidate_lock_shared(mapping);
> > + min_order = mapping_min_folio_order(mapping);
> > + index = (pos >> (min_order + PAGE_SHIFT)) << min_order;
>
> That is some cool mathfu. I will add a comment here as it might not be
> that obvious to some people (i.e me).
you guys are both wrong, just use rounddown()
