[PATCH v4 03/11] filemap: allocate mapping_min_order folios in the page cache

Pankaj Raghav (Samsung)
2024-04-25T11:38:11Z

From: Luis Chamberlain <mcgrof@kernel.org>

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.

Supporting mapping_min_order implies that we guarantee each folio in the
page cache has at least an order of mapping_min_order. When adding new
folios to the page cache we must also 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.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Co-developed-by: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
---
mm/filemap.c | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 30de18c4fd28..f0c0cfbbd134 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -858,6 +858,8 @@ noinline int __filemap_add_folio(struct address_space *mapping,

VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
VM_BUG_ON_FOLIO(folio_test_swapbacked(folio), folio);
+ VM_BUG_ON_FOLIO(folio_order(folio) < mapping_min_folio_order(mapping),
+ folio);
mapping_set_update(&xas, mapping);

if (!huge) {
@@ -1895,8 +1897,10 @@ 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 min_order = mapping_min_folio_order(mapping);
+ unsigned int order = max(min_order, FGF_GET_ORDER(fgp_flags));
int err;
+ index = mapping_align_start_index(mapping, index);

if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
gfp |= __GFP_WRITE;
@@ -1936,7 +1940,7 @@ 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;
@@ -2425,13 +2429,16 @@ 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)
{
struct folio *folio;
int error;
+ unsigned int min_order = mapping_min_folio_order(mapping);
+ pgoff_t index;

- folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
+ folio = filemap_alloc_folio(mapping_gfp_mask(mapping),
+ min_order);
if (!folio)
return -ENOMEM;

@@ -2449,6 +2456,8 @@ static int filemap_create_folio(struct file *file,
* well to keep locking rules simple.
*/
filemap_invalidate_lock_shared(mapping);
+ /* index in PAGE units but aligned to min_order number of pages. */
+ index = (pos >> (PAGE_SHIFT + min_order)) << min_order;
error = filemap_add_folio(mapping, folio, index,
mapping_gfp_constraint(mapping, GFP_KERNEL));
if (error == -EEXIST)
@@ -2509,8 +2518,7 @@ 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;
@@ -3708,9 +3716,11 @@ 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);
+ index = mapping_align_start_index(mapping, index);
err = filemap_add_folio(mapping, folio, index, gfp);
if (unlikely(err)) {
folio_put(folio);
--
2.34.1