[v21,08/30] splice: Make splice from a DAX file use copy_splice_read()

Commit Message

David Howells May 20, 2023, midnight UTC

Make a read splice from a DAX file go directly to copy_splice_read() to do
the reading as filemap_splice_read() is unlikely to find any pagecache to
splice.

I think this affects only erofs, Ext2, Ext4, fuse and XFS.

Signed-off-by: David Howells <[e-mail]>
cc: Christoph Hellwig <[e-mail]>
cc: Al Viro <[e-mail]>
cc: Jens Axboe <[e-mail]>
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
---

Notes:
    ver #21)
     - Don't need #ifdef CONFIG_FS_DAX as IS_DAX() is false if !CONFIG_FS_DAX.
     - Needs to be in vfs_splice_read(), not generic_file_splice_read().

 fs/splice.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

Christoph Hellwig May 20, 2023, 4:11 a.m. UTC | #1

Looks good:

Reviewed-by: Christoph Hellwig <[e-mail]>

Christian Brauner May 20, 2023, 9:41 a.m. UTC | #2

On Sat, May 20, 2023 at 01:00:27AM +0100, David Howells wrote:
> Make a read splice from a DAX file go directly to copy_splice_read() to do
> the reading as filemap_splice_read() is unlikely to find any pagecache to
> splice.
> 
> I think this affects only erofs, Ext2, Ext4, fuse and XFS.
> 
> Signed-off-by: David Howells <[e-mail]>
> cc: Christoph Hellwig <[e-mail]>
> cc: Al Viro <[e-mail]>
> cc: Jens Axboe <[e-mail]>
> cc: [e-mail]
> cc: [e-mail]
> cc: [e-mail]
> cc: [e-mail]
> cc: [e-mail]
> cc: [e-mail]
> ---

Fwiw, O_DIRECT and DAX could've just been folded into one patch imho.
Reviewed-by: Christian Brauner <[e-mail]>

Theodore Ts'o May 21, 2023, 12:28 a.m. UTC | #3

On Sat, May 20, 2023 at 01:00:27AM +0100, David Howells wrote:
> Make a read splice from a DAX file go directly to copy_splice_read() to do
> the reading as filemap_splice_read() is unlikely to find any pagecache to
> splice.
> 
> I think this affects only erofs, Ext2, Ext4, fuse and XFS.
> 
> Signed-off-by: David Howells <[e-mail]>
> cc: Christoph Hellwig <[e-mail]>
> cc: Al Viro <[e-mail]>
> cc: Jens Axboe <[e-mail]>
> cc: [e-mail]
> cc: [e-mail]

Reviewed-by: Theodore Ts'o <[e-mail]>

Gao Xiang May 21, 2023, 2:55 p.m. UTC | #4

On 2023/5/20 17:00, David Howells wrote:
> Make a read splice from a DAX file go directly to copy_splice_read() to do
> the reading as filemap_splice_read() is unlikely to find any pagecache to
> splice.
> 
> I think this affects only erofs, Ext2, Ext4, fuse and XFS.
> 
> Signed-off-by: David Howells <[e-mail]>
> cc: Christoph Hellwig <[e-mail]>
> cc: Al Viro <[e-mail]>
> cc: Jens Axboe <[e-mail]>
> cc: [e-mail]
> cc: [e-mail]
> cc: [e-mail]
> cc: [e-mail]
> cc: [e-mail]
> cc: [e-mail]

Reviewed-by: Gao Xiang <[e-mail]>

Thanks,
Gao Xiang

Patch

diff --git a/fs/splice.c b/fs/splice.c
index 76126b1aafcb..8268248df3a9 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -908,10 +908,10 @@  long vfs_splice_read(struct file *in, loff_t *ppos,
 	if (unlikely(!in->f_op->splice_read))
 		return warn_unsupported(in, "read");
 	/*
-	 * O_DIRECT doesn't deal with the pagecache, so we allocate a buffer,
-	 * copy into it and splice that into the pipe.
+	 * O_DIRECT and DAX don't deal with the pagecache, so we allocate a
+	 * buffer, copy into it and splice that into the pipe.
 	 */
-	if ((in->f_flags & O_DIRECT))
+	if ((in->f_flags & O_DIRECT) || IS_DAX(in->f_mapping->host))
 		return copy_splice_read(in, ppos, pipe, len, flags);
 	return in->f_op->splice_read(in, ppos, pipe, len, flags);
 }