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

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