Re: [RFC PATCH v2] mm, netfs, fscache: Stop read optimisation when folio removed from pagecache

Matthew Wilcox
2022-11-15T04:09:27Z

On Mon, Nov 14, 2022 at 04:02:20PM +0000, David Howells wrote:
> +++ b/mm/filemap.c
> @@ -3941,6 +3941,10 @@ bool filemap_release_folio(struct folio *folio, gfp_t gfp)
> struct address_space * const mapping = folio->mapping;
>
> BUG_ON(!folio_test_locked(folio));
> + if ((!mapping || !mapping_release_always(mapping))
> + && !folio_test_private(folio) &&
> + !folio_test_private_2(folio))
> + return true;

Why do you need to test 'mapping' here? Also this is the most
inconsistent style ...

if ((!mapping || !mapping_release_always(mapping)) &&
!folio_test_private(folio) && !folio_test_private_2(folio))

works fine, but if you insist on splitting over three lines, then:

if ((!mapping || !mapping_release_always(mapping)) &&
!folio_test_private(folio) &&
!folio_test_private_2(folio))

> @@ -276,7 +275,7 @@ static long mapping_evict_folio(struct address_space *mapping,
> if (folio_ref_count(folio) >
> folio_nr_pages(folio) + folio_has_private(folio) + 1)

I think this line is incorrect, right? You don't increment the folio
refcount just because the folio has private2 set, do you?

> return 0;
> - if (folio_has_private(folio) && !filemap_release_folio(folio, 0))
> + if (!filemap_release_folio(folio, 0))
> return 0;
>
> return remove_mapping(mapping, folio);

Can we get rid of folio_has_private() / page_has_private() now?