Ocfs2 devel - May 2023 - [PATCH v21 22/30] ocfs2: Provide a splice-read stub

Provide a splice_read stub for ocfs2.  This emits trace lines and does an
atime lock/update before calling filemap_splice_read().  Splicing from
direct I/O is handled by the caller.

A couple of new tracepoints are added for this purpose.

Signed-off-by: David Howells <dhowells at redhat.com>
cc: Christoph Hellwig <hch at lst.de>
cc: Al Viro <viro at zeniv.linux.org.uk>
cc: Jens Axboe <axboe at kernel.dk>
cc: Mark Fasheh <mark at fasheh.com>
cc: Joel Becker <jlbec at evilplan.org>
cc: Joseph Qi <joseph.qi at linux.alibaba.com>
cc: ocfs2-devel at oss.oracle.com
cc: linux-fsdevel at vger.kernel.org
cc: linux-block at vger.kernel.org
cc: linux-mm at kvack.org
---
 fs/ocfs2/file.c        | 39 ++++++++++++++++++++++++++++++++++++++-
 fs/ocfs2/ocfs2_trace.h |  3 +++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index efb09de4343d..f7e00b5689d5 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -2581,6 +2581,43 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
 	return ret;
 }
 
+static ssize_t ocfs2_file_splice_read(struct file *in, loff_t *ppos,
+				      struct pipe_inode_info *pipe,
+				      size_t len, unsigned int flags)
+{
+	struct inode *inode = file_inode(in);
+	ssize_t ret = 0;
+	int lock_level = 0;
+
+	trace_ocfs2_file_splice_read(inode, in, in->f_path.dentry,
+				     (unsigned long long)OCFS2_I(inode)->ip_blkno,
+				     in->f_path.dentry->d_name.len,
+				     in->f_path.dentry->d_name.name,
+				     0);
+
+	/*
+	 * We're fine letting folks race truncates and extending writes with
+	 * read across the cluster, just like they can locally.  Hence no
+	 * rw_lock during read.
+	 *
+	 * Take and drop the meta data lock to update inode fields like i_size.
+	 * This allows the checks down below generic_file_splice_read() a
+	 * chance of actually working.
+	 */
+	ret = ocfs2_inode_lock_atime(inode, in->f_path.mnt, &lock_level, true);
+	if (ret < 0) {
+		if (ret != -EAGAIN)
+			mlog_errno(ret);
+		goto bail;
+	}
+	ocfs2_inode_unlock(inode, lock_level);
+
+	ret = filemap_splice_read(in, ppos, pipe, len, flags);
+	trace_filemap_splice_read_ret(ret);
+bail:
+	return ret;
+}
+
 /* Refer generic_file_llseek_unlocked() */
 static loff_t ocfs2_file_llseek(struct file *file, loff_t offset, int whence)
 {
@@ -2744,7 +2781,7 @@ const struct file_operations ocfs2_fops = {
 #endif
 	.lock		= ocfs2_lock,
 	.flock		= ocfs2_flock,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= ocfs2_file_splice_read,
 	.splice_write	= iter_file_splice_write,
 	.fallocate	= ocfs2_fallocate,
 	.remap_file_range = ocfs2_remap_file_range,
diff --git a/fs/ocfs2/ocfs2_trace.h b/fs/ocfs2/ocfs2_trace.h
index dc4bce1649c1..b8c3d1702076 100644
--- a/fs/ocfs2/ocfs2_trace.h
+++ b/fs/ocfs2/ocfs2_trace.h
@@ -1319,6 +1319,8 @@ DEFINE_OCFS2_FILE_OPS(ocfs2_file_splice_write);
 
 DEFINE_OCFS2_FILE_OPS(ocfs2_file_read_iter);
 
+DEFINE_OCFS2_FILE_OPS(ocfs2_file_splice_read);
+
 DEFINE_OCFS2_ULL_ULL_ULL_EVENT(ocfs2_truncate_file);
 
 DEFINE_OCFS2_ULL_ULL_EVENT(ocfs2_truncate_file_error);
@@ -1470,6 +1472,7 @@ TRACE_EVENT(ocfs2_prepare_inode_for_write,
 );
 
 DEFINE_OCFS2_INT_EVENT(generic_file_read_iter_ret);
+DEFINE_OCFS2_INT_EVENT(filemap_splice_read_ret);
 
 /* End of trace events for fs/ocfs2/file.c. */

On 5/20/23 8:00 AM, David Howells wrote:
> Provide a splice_read stub for ocfs2.  This emits trace lines and does an
> atime lock/update before calling filemap_splice_read().  Splicing from
> direct I/O is handled by the caller.
> 
> A couple of new tracepoints are added for this purpose.
> 
> Signed-off-by: David Howells <dhowells at redhat.com>
> cc: Christoph Hellwig <hch at lst.de>
> cc: Al Viro <viro at zeniv.linux.org.uk>
> cc: Jens Axboe <axboe at kernel.dk>
> cc: Mark Fasheh <mark at fasheh.com>
> cc: Joel Becker <jlbec at evilplan.org>
> cc: Joseph Qi <joseph.qi at linux.alibaba.com>
> cc: ocfs2-devel at oss.oracle.com
> cc: linux-fsdevel at vger.kernel.org
> cc: linux-block at vger.kernel.org
> cc: linux-mm at kvack.org
> ---
>  fs/ocfs2/file.c        | 39 ++++++++++++++++++++++++++++++++++++++-
>  fs/ocfs2/ocfs2_trace.h |  3 +++
>  2 files changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> index efb09de4343d..f7e00b5689d5 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -2581,6 +2581,43 @@ static ssize_t ocfs2_file_read_iter(struct kiocb
*iocb,
>  	return ret;
>  }
>  
> +static ssize_t ocfs2_file_splice_read(struct file *in, loff_t *ppos,
> +				      struct pipe_inode_info *pipe,
> +				      size_t len, unsigned int flags)
> +{
> +	struct inode *inode = file_inode(in);
> +	ssize_t ret = 0;
> +	int lock_level = 0;
> +
> +	trace_ocfs2_file_splice_read(inode, in, in->f_path.dentry,
> +				     (unsigned long long)OCFS2_I(inode)->ip_blkno,
> +				     in->f_path.dentry->d_name.len,
> +				     in->f_path.dentry->d_name.name,
> +				     0);
Better also trace flags here.
> +
> +	/*
> +	 * We're fine letting folks race truncates and extending writes with
> +	 * read across the cluster, just like they can locally.  Hence no
> +	 * rw_lock during read.
> +	 *
> +	 * Take and drop the meta data lock to update inode fields like i_size.
> +	 * This allows the checks down below generic_file_splice_read() a
Now it calls filemap_splice_read().
> +	 * chance of actually working.
> +	 */
> +	ret = ocfs2_inode_lock_atime(inode, in->f_path.mnt, &lock_level,
true);
Since prototype is 'int wait', so directly passing '1' seems
more appropriate.
> +	if (ret < 0) {
> +		if (ret != -EAGAIN)
> +			mlog_errno(ret);
> +		goto bail;
> +	}
> +	ocfs2_inode_unlock(inode, lock_level);
> +
Don't see direct IO logic now. Am I missing something?

Thanks,
Joseph
> +	ret = filemap_splice_read(in, ppos, pipe, len, flags);
> +	trace_filemap_splice_read_ret(ret);
> +bail:
> +	return ret;
> +}
> +
>  /* Refer generic_file_llseek_unlocked() */
>  static loff_t ocfs2_file_llseek(struct file *file, loff_t offset, int
whence)
>  {
> @@ -2744,7 +2781,7 @@ const struct file_operations ocfs2_fops = {
>  #endif
>  	.lock		= ocfs2_lock,
>  	.flock		= ocfs2_flock,
> -	.splice_read	= generic_file_splice_read,
> +	.splice_read	= ocfs2_file_splice_read,
>  	.splice_write	= iter_file_splice_write,
>  	.fallocate	= ocfs2_fallocate,
>  	.remap_file_range = ocfs2_remap_file_range,
> diff --git a/fs/ocfs2/ocfs2_trace.h b/fs/ocfs2/ocfs2_trace.h
> index dc4bce1649c1..b8c3d1702076 100644
> --- a/fs/ocfs2/ocfs2_trace.h
> +++ b/fs/ocfs2/ocfs2_trace.h
> @@ -1319,6 +1319,8 @@ DEFINE_OCFS2_FILE_OPS(ocfs2_file_splice_write);
>  
>  DEFINE_OCFS2_FILE_OPS(ocfs2_file_read_iter);
>  
> +DEFINE_OCFS2_FILE_OPS(ocfs2_file_splice_read);
> +
>  DEFINE_OCFS2_ULL_ULL_ULL_EVENT(ocfs2_truncate_file);
>  
>  DEFINE_OCFS2_ULL_ULL_EVENT(ocfs2_truncate_file_error);
> @@ -1470,6 +1472,7 @@ TRACE_EVENT(ocfs2_prepare_inode_for_write,
>  );
>  
>  DEFINE_OCFS2_INT_EVENT(generic_file_read_iter_ret);
> +DEFINE_OCFS2_INT_EVENT(filemap_splice_read_ret);
>  
>  /* End of trace events for fs/ocfs2/file.c. */
>

Joseph Qi <joseph.qi at linux.alibaba.com> wrote:
> Don't see direct IO logic now. Am I missing something?
See that patch description ;-)

    Provide a splice_read stub for ocfs2.  This emits trace lines and does an
    atime lock/update before calling filemap_splice_read().  Splicing from
    direct I/O is handled by the caller.

David

So something like the attached changes?  Any suggestions as to how to improve
the comments?

David
---
diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index f7e00b5689d5..86add13b5f23 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -2552,7 +2552,7 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
 	 *
 	 * Take and drop the meta data lock to update inode fields
 	 * like i_size. This allows the checks down below
-	 * generic_file_read_iter() a chance of actually working.
+	 * copy_splice_read() a chance of actually working.
 	 */
 	ret = ocfs2_inode_lock_atime(inode, filp->f_path.mnt, &lock_level,
 				     !nowait);
@@ -2593,7 +2593,7 @@ static ssize_t ocfs2_file_splice_read(struct file *in,
loff_t *ppos,
 				     (unsigned long long)OCFS2_I(inode)->ip_blkno,
 				     in->f_path.dentry->d_name.len,
 				     in->f_path.dentry->d_name.name,
-				     0);
+				     flags);
 
 	/*
 	 * We're fine letting folks race truncates and extending writes with
@@ -2601,10 +2601,10 @@ static ssize_t ocfs2_file_splice_read(struct file *in,
loff_t *ppos,
 	 * rw_lock during read.
 	 *
 	 * Take and drop the meta data lock to update inode fields like i_size.
-	 * This allows the checks down below generic_file_splice_read() a
-	 * chance of actually working.
+	 * This allows the checks down below filemap_splice_read() a chance of
+	 * actually working.
 	 */
-	ret = ocfs2_inode_lock_atime(inode, in->f_path.mnt, &lock_level, true);
+	ret = ocfs2_inode_lock_atime(inode, in->f_path.mnt, &lock_level, 1);
 	if (ret < 0) {
 		if (ret != -EAGAIN)
 			mlog_errno(ret);