[RFC PATCH 1/1] Remove buffered failover for ext4 and block fops direct writes.

Jeremy Bongio
2024-05-01T23:16:24Z

From: Jeremy Bongio <jbongio@google.com>

ext4 and block fops would both failover to syncronous, buffered writes if
the direct IO results in a short write where only a portion of the request
was completed.

This patch changes the behavior to simply return the number of bytes
written if the direct write is short.
---
block/fops.c | 3 ---
fs/ext4/file.c | 27 ---------------------------
2 files changed, 30 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index 0cf8cf72cdfa..d32574ba9d71 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -704,9 +704,6 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)

if (iocb->ki_flags & IOCB_DIRECT) {
ret = blkdev_direct_write(iocb, from);
- if (ret >= 0 && iov_iter_count(from))
- ret = direct_write_fallback(iocb, from, ret,
- blkdev_buffered_write(iocb, from));
} else {
ret = blkdev_buffered_write(iocb, from);
}
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 54d6ff22585c..d0760452a11f 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -595,32 +595,6 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
else
inode_unlock(inode);

- if (ret >= 0 && iov_iter_count(from)) {
- ssize_t err;
- loff_t endbyte;
-
- offset = iocb->ki_pos;
- err = ext4_buffered_write_iter(iocb, from);
- if (err < 0)
- return err;
-
- /*
- * We need to ensure that the pages within the page cache for
- * the range covered by this I/O are written to disk and
- * invalidated. This is in attempt to preserve the expected
- * direct I/O semantics in the case we fallback to buffered I/O
- * to complete off the I/O request.
- */
- ret += err;
- endbyte = offset + err - 1;
- err = filemap_write_and_wait_range(iocb->ki_filp->f_mapping,
- offset, endbyte);
- if (!err)
- invalidate_mapping_pages(iocb->ki_filp->f_mapping,
- offset >> PAGE_SHIFT,
- endbyte >> PAGE_SHIFT);
- }
-
return ret;
}

@@ -958,4 +932,3 @@ const struct inode_operations ext4_file_inode_operations = {
.fileattr_get = ext4_fileattr_get,
.fileattr_set = ext4_fileattr_set,
};
-
--
2.44.0.769.g3c40516874-goog