Re: [RFC v2 03/14] filemap: use mapping_min_order while allocating folios

Darrick J. Wong
2024-02-13T16:38:30Z

On Tue, Feb 13, 2024 at 10:37:02AM +0100, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
>
> filemap_create_folio() and do_read_cache_folio() were always allocating
> folio of order 0. __filemap_get_folio was trying to allocate higher
> order folios when fgp_flags had higher order hint set but it will default
> to order 0 folio if higher order memory allocation fails.
>
> As we bring the notion of mapping_min_order, make sure these functions
> allocate at least folio of mapping_min_order as we need to guarantee it
> in the page cache.
>
> Add some additional VM_BUG_ON() in page_cache_delete[batch] and
> __filemap_add_folio to catch errors where we delete or add folios that
> has order less than min_order.
>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

Looks good to me,
Acked-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
> mm/filemap.c | 25 +++++++++++++++++++++----
> 1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 323a8e169581..7a6e15c47150 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -127,6 +127,7 @@
> static void page_cache_delete(struct address_space *mapping,
> struct folio *folio, void *shadow)
> {
> + unsigned int min_order = mapping_min_folio_order(mapping);
> XA_STATE(xas, &mapping->i_pages, folio->index);
> long nr = 1;
>
> @@ -135,6 +136,7 @@ static void page_cache_delete(struct address_space *mapping,
> xas_set_order(&xas, folio->index, folio_order(folio));
> nr = folio_nr_pages(folio);
>
> + VM_BUG_ON_FOLIO(folio_order(folio) < min_order, folio);
> VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
>
> xas_store(&xas, shadow);
> @@ -277,6 +279,7 @@ void filemap_remove_folio(struct folio *folio)
> static void page_cache_delete_batch(struct address_space *mapping,
> struct folio_batch *fbatch)
> {
> + unsigned int min_order = mapping_min_folio_order(mapping);
> XA_STATE(xas, &mapping->i_pages, fbatch->folios[0]->index);
> long total_pages = 0;
> int i = 0;
> @@ -305,6 +308,7 @@ static void page_cache_delete_batch(struct address_space *mapping,
>
> WARN_ON_ONCE(!folio_test_locked(folio));
>
> + VM_BUG_ON_FOLIO(folio_order(folio) < min_order, folio);
> folio->mapping = NULL;
> /* Leave folio->index set: truncation lookup relies on it */
>
> @@ -846,6 +850,7 @@ noinline int __filemap_add_folio(struct address_space *mapping,
> int huge = folio_test_hugetlb(folio);
> bool charged = false;
> long nr = 1;
> + unsigned int min_order = mapping_min_folio_order(mapping);
>
> VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
> VM_BUG_ON_FOLIO(folio_test_swapbacked(folio), folio);
> @@ -896,6 +901,7 @@ noinline int __filemap_add_folio(struct address_space *mapping,
> }
> }
>
> + VM_BUG_ON_FOLIO(folio_order(folio) < min_order, folio);
> xas_store(&xas, folio);
> if (xas_error(&xas))
> goto unlock;
> @@ -1847,6 +1853,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> fgf_t fgp_flags, gfp_t gfp)
> {
> struct folio *folio;
> + unsigned int min_order = mapping_min_folio_order(mapping);
> + unsigned int min_nrpages = mapping_min_folio_nrpages(mapping);
> +
> + index = round_down(index, min_nrpages);
>
> repeat:
> folio = filemap_get_entry(mapping, index);
> @@ -1886,7 +1896,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> folio_wait_stable(folio);
> no_page:
> if (!folio && (fgp_flags & FGP_CREAT)) {
> - unsigned order = FGF_GET_ORDER(fgp_flags);
> + unsigned int order = max(min_order, FGF_GET_ORDER(fgp_flags));
> int err;
>
> if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
> @@ -1914,8 +1924,13 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> err = -ENOMEM;
> if (order == 1)
> order = 0;
> + if (order < min_order)
> + order = min_order;
> if (order > 0)
> alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
> +
> + VM_BUG_ON(index & ((1UL << order) - 1));
> +
> folio = filemap_alloc_folio(alloc_gfp, order);
> if (!folio)
> continue;
> @@ -1929,7 +1944,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
> break;
> folio_put(folio);
> folio = NULL;
> - } while (order-- > 0);
> + } while (order-- > min_order);
>
> if (err == -EEXIST)
> goto repeat;
> @@ -2424,7 +2439,8 @@ static int filemap_create_folio(struct file *file,
> struct folio *folio;
> int error;
>
> - folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
> + folio = filemap_alloc_folio(mapping_gfp_mask(mapping),
> + mapping_min_folio_order(mapping));
> if (!folio)
> return -ENOMEM;
>
> @@ -3682,7 +3698,8 @@ static struct folio *do_read_cache_folio(struct address_space *mapping,
> repeat:
> folio = filemap_get_folio(mapping, index);
> if (IS_ERR(folio)) {
> - folio = filemap_alloc_folio(gfp, 0);
> + folio = filemap_alloc_folio(gfp,
> + mapping_min_folio_order(mapping));
> if (!folio)
> return ERR_PTR(-ENOMEM);
> err = filemap_add_folio(mapping, folio, index, gfp);
> --
> 2.43.0
>
>