[PATCH 09/12] mm/filemap: drop uncached pages when writeback completes

Jens Axboe
2024-12-03T15:32:59Z

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 139d1db79ff8..eb6a8d39f9d0 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1599,6 +1599,27 @@ 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.
@@ -1609,6 +1630,8 @@ 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);

/*
@@ -1630,9 +1653,14 @@ void folio_end_writeback(struct folio *folio)
* reused before the folio_wake_bit().
*/
folio_get(folio);
+ if (!folio_test_dirty(folio))
+ 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