2023-09-15 21:07:28

by Matthew Wilcox

Subject: Re: [RFC 05/23] filemap: align index to mapping_min_order in filemap_range_has_page()

On Fri, Sep 15, 2023 at 08:38:30PM +0200, Pankaj Raghav wrote:
> From: Luis Chamberlain <[email protected]>
>
> page cache is mapping min_folio_order aligned. Use mapping min_folio_order
> to align the start_byte and end_byte in filemap_range_has_page().

What goes wrong if you don't? Seems to me like it should work.

> Signed-off-by: Luis Chamberlain <[email protected]>
> ---
> mm/filemap.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 2c47729dc8b0..4dee24b5b61c 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -477,9 +477,12 @@ EXPORT_SYMBOL(filemap_flush);
> bool filemap_range_has_page(struct address_space *mapping,
> loff_t start_byte, loff_t end_byte)
> {
> + unsigned int min_order = mapping_min_folio_order(mapping);
> + unsigned int nrpages = 1UL << min_order;
> + pgoff_t index = round_down(start_byte >> PAGE_SHIFT, nrpages);
> struct folio *folio;
> - XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
> - pgoff_t max = end_byte >> PAGE_SHIFT;
> + XA_STATE(xas, &mapping->i_pages, index);
> + pgoff_t max = round_down(end_byte >> PAGE_SHIFT, nrpages);
>
> if (end_byte < start_byte)
> return false;
> --
> 2.40.1
>

2023-09-19 00:00:59

by Luis Chamberlain

Subject: Re: [RFC 05/23] filemap: align index to mapping_min_order in filemap_range_has_page()

On Fri, Sep 15, 2023 at 08:45:20PM +0100, Matthew Wilcox wrote:
> On Fri, Sep 15, 2023 at 08:38:30PM +0200, Pankaj Raghav wrote:
> > From: Luis Chamberlain <[email protected]>
> >
> > page cache is mapping min_folio_order aligned. Use mapping min_folio_order
> > to align the start_byte and end_byte in filemap_range_has_page().
>
> What goes wrong if you don't? Seems to me like it should work.

Will drop from the series after confirming, thanks.

Luis