linux-ext4 - [PATCH 09/16] mm/filemap: drop uncached pages when writeback completes

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Message-ID: <20241111234842.2024180-10-axboe@kernel.dk>
Date: Mon, 11 Nov 2024 16:37:36 -0700
From: Jens Axboe <axboe@...nel.dk>
To: linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org
Cc: hannes@...xchg.org,
	clm@...a.com,
	linux-kernel@...r.kernel.org,
	willy@...radead.org,
	kirill@...temov.name,
	linux-btrfs@...r.kernel.org,
	linux-ext4@...r.kernel.org,
	linux-xfs@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 09/16] mm/filemap: drop uncached pages when writeback completes

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@...nel.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;
 	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