linux-ext4 - [PATCH 06/10] libext2fs: only flush affected blocks in unix_write

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Message-ID: <175573713442.21546.1469237500636906426.stgit@frogsfrogsfrogs>
Date: Wed, 20 Aug 2025 18:14:38 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: John@...ves.net, bernd@...ernd.com, linux-fsdevel@...r.kernel.org,
 linux-ext4@...r.kernel.org, miklos@...redi.hu, joannelkoong@...il.com,
 neal@...pa.dev
Subject: [PATCH 06/10] libext2fs: only flush affected blocks in
 unix_write_byte

From: Darrick J. Wong <djwong@...nel.org>

There's no need to invalidate the entire cache when writing a range of
bytes to the device.  The only ones we need to invalidate are the ones
that we're writing separately.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 lib/ext2fs/unix_io.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
index 0d1006207c60cd..4036c4b6f1481e 100644
--- a/lib/ext2fs/unix_io.c
+++ b/lib/ext2fs/unix_io.c
@@ -1469,6 +1469,7 @@ static errcode_t unix_write_byte(io_channel channel, unsigned long offset,
 {
 	struct unix_private_data *data;
 	errcode_t	retval = 0;
+	unsigned long long bno, nbno;
 	ssize_t		actual;

 	EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
@@ -1484,10 +1485,17 @@ static errcode_t unix_write_byte(io_channel channel, unsigned long offset,

 #ifndef NO_IO_CACHE
 	/*
-	 * Flush out the cache completely
+	 * Flush all the dirty blocks, then invalidate the blocks we're about
+	 * to write.
 	 */
-	if ((retval = flush_cached_blocks(channel, data, FLUSH_INVALIDATE)))
+	retval = flush_cached_blocks(channel, data, 0);
+	if (retval)
 		return retval;
+
+	bno = offset / channel->block_size;
+	nbno = (offset + size + channel->block_size - 1) / channel->block_size;
+
+	invalidate_cached_blocks(channel, data, bno, nbno - bno);
 #endif

 	if (lseek(data->dev, offset + data->offset, SEEK_SET) < 0)