Re: [PATCH 09/16] mm/filemap: drop uncached pages when writeback completes

Kirill A. Shutemov
2024-11-12T09:31:57Z

On Mon, Nov 11, 2024 at 04:37:36PM -0700, Jens Axboe wrote:
> If the folio is marked as uncached, drop pages when writeback completes.
> Intended to be used with RWF_UNCACHED, to avoid needing sync writes for
> uncached IO.
>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
> mm/filemap.c | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 3d0614ea5f59..40debe742abe 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1600,6 +1600,27 @@ int folio_wait_private_2_killable(struct folio *folio)
> }
> EXPORT_SYMBOL(folio_wait_private_2_killable);
>
> +/*
> + * If folio was marked as uncached, then pages should be dropped when writeback
> + * completes. Do that now. If we fail, it's likely because of a big folio -
> + * just reset uncached for that case and latter completions should invalidate.
> + */
> +static void folio_end_uncached(struct folio *folio)
> +{
> + /*
> + * Hitting !in_task() should not happen off RWF_UNCACHED writeback, but
> + * can happen if normal writeback just happens to find dirty folios
> + * that were created as part of uncached writeback, and that writeback
> + * would otherwise not need non-IRQ handling. Just skip the
> + * invalidation in that case.
> + */
> + if (in_task() && folio_trylock(folio)) {
> + if (folio->mapping)
> + folio_unmap_invalidate(folio->mapping, folio, 0);
> + folio_unlock(folio);
> + }
> +}
> +
> /**
> * folio_end_writeback - End writeback against a folio.
> * @folio: The folio.
> @@ -1610,6 +1631,8 @@ EXPORT_SYMBOL(folio_wait_private_2_killable);
> */
> void folio_end_writeback(struct folio *folio)
> {
> + bool folio_uncached = false;
> +
> VM_BUG_ON_FOLIO(!folio_test_writeback(folio), folio);
>
> /*
> @@ -1631,9 +1654,14 @@ void folio_end_writeback(struct folio *folio)
> * reused before the folio_wake_bit().
> */
> folio_get(folio);
> + if (folio_test_uncached(folio) && folio_test_clear_uncached(folio))
> + folio_uncached = true;

Hm? Maybe

folio_uncached = folio_test_clear_uncached(folio);

?

> if (__folio_end_writeback(folio))
> folio_wake_bit(folio, PG_writeback);
> acct_reclaim_writeback(folio);
> +
> + if (folio_uncached)
> + folio_end_uncached(folio);
> folio_put(folio);
> }
> EXPORT_SYMBOL(folio_end_writeback);
> --
> 2.45.2
>

--
Kiryl Shutsemau / Kirill A. Shutemov