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;
