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). Thanks. > error = filemap_add_folio(mapping, folio, index, > mapping_gfp_constraint(mapping, GFP_KERNEL)); > if (error == -EEXIST) > @@ -2511,8 +2515,7 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count, > if (!folio_batch_count(fbatch)) { > if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ)) > return -EAGAIN; > - err = filemap_create_folio(filp, mapping, > - iocb->ki_pos >> PAGE_SHIFT, fbatch); > + err = filemap_create_folio(filp, mapping, iocb->ki_pos, fbatch); > if (err == AOP_TRUNCATED_PAGE) > goto retry; > return err;