[v2,1/6] ext4: introduce direct IO read path using iomap infrastructure
diff mbox series

Message ID 75a6ead09a10e362526a849af482510a0090f82a.1567978633.git.mbobrowski@mbobrowski.org
State New
Headers show
Series
  • ext4: port direct IO to iomap infrastructure
Related show

Commit Message

Matthew Bobrowski Sept. 8, 2019, 11:18 p.m. UTC
This patch introduces a new direct IO read path that makes use of the
iomap infrastructure.

The new function ext4_dio_read_iter() is responsible for calling into
the iomap infrastructure via iomap_dio_rw(). If the inode in question
does not pass preliminary checks in ext4_dio_checks(), then we simply
fallback to buffered IO and take that path to fulfil the request. It's
imperative that we drop the IOCB_DIRECT flag from iocb->ki_flags in
order to prevent generic_file_read_iter() from trying to take the
direct IO code path again.

Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
---
 fs/ext4/file.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 54 insertions(+), 4 deletions(-)

Comments

Ritesh Harjani Sept. 9, 2019, 7:48 a.m. UTC | #1
On 9/9/19 4:48 AM, Matthew Bobrowski wrote:
> This patch introduces a new direct IO read path that makes use of the
> iomap infrastructure.
> 
> The new function ext4_dio_read_iter() is responsible for calling into
> the iomap infrastructure via iomap_dio_rw(). If the inode in question
> does not pass preliminary checks in ext4_dio_checks(), then we simply
> fallback to buffered IO and take that path to fulfil the request. It's
> imperative that we drop the IOCB_DIRECT flag from iocb->ki_flags in
> order to prevent generic_file_read_iter() from trying to take the
> direct IO code path again.
> 
> Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>

Looks good to me.

Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>

> ---
>   fs/ext4/file.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++----
>   1 file changed, 54 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 70b0438dbc94..e52e3928dc25 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -34,6 +34,53 @@
>   #include "xattr.h"
>   #include "acl.h"
> 
> +static bool ext4_dio_checks(struct inode *inode)
> +{
> +#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
> +	if (IS_ENCRYPTED(inode))
> +		return false;
> +#endif
> +	if (ext4_should_journal_data(inode))
> +		return false;
> +	if (ext4_has_inline_data(inode))
> +		return false;
> +	return true;
> +}
> +
> +static ssize_t ext4_dio_read_iter(struct kiocb *iocb, struct iov_iter *to)
> +{
> +	ssize_t ret;
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +
> +	/*
> +	 * Get exclusion from truncate and other inode operations.
> +	 */
> +	if (!inode_trylock_shared(inode)) {
> +		if (iocb->ki_flags & IOCB_NOWAIT)
> +			return -EAGAIN;
> +		inode_lock_shared(inode);
> +	}
> +
> +	if (!ext4_dio_checks(inode)) {
> +		inode_unlock_shared(inode);
> +		/*
> +		 * Fallback to buffered IO if the operation being
> +		 * performed on the inode is not supported by direct
> +		 * IO. The IOCB_DIRECT flag flags needs to be cleared
> +		 * here to ensure that the direct IO code path within
> +		 * generic_file_read_iter() is not taken again.
> +		 */
> +		iocb->ki_flags &= ~IOCB_DIRECT;
> +		return generic_file_read_iter(iocb, to);
> +	}
> +
> +	ret = iomap_dio_rw(iocb, to, &ext4_iomap_ops, NULL);
> +	inode_unlock_shared(inode);
> +
> +	file_accessed(iocb->ki_filp);
> +	return ret;
> +}
> +
>   #ifdef CONFIG_FS_DAX
>   static ssize_t ext4_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
>   {
> @@ -64,16 +111,19 @@ static ssize_t ext4_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
> 
>   static ssize_t ext4_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
>   {
> -	if (unlikely(ext4_forced_shutdown(EXT4_SB(file_inode(iocb->ki_filp)->i_sb))))
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +
> +	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
>   		return -EIO;
> 
>   	if (!iov_iter_count(to))
>   		return 0; /* skip atime */
> 
> -#ifdef CONFIG_FS_DAX
> -	if (IS_DAX(file_inode(iocb->ki_filp)))
> +	if (IS_DAX(inode))
>   		return ext4_dax_read_iter(iocb, to);
> -#endif
> +
> +	if (iocb->ki_flags & IOCB_DIRECT)
> +		return ext4_dio_read_iter(iocb, to);
>   	return generic_file_read_iter(iocb, to);
>   }
>

Patch
diff mbox series

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 70b0438dbc94..e52e3928dc25 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -34,6 +34,53 @@ 
 #include "xattr.h"
 #include "acl.h"
 
+static bool ext4_dio_checks(struct inode *inode)
+{
+#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
+	if (IS_ENCRYPTED(inode))
+		return false;
+#endif
+	if (ext4_should_journal_data(inode))
+		return false;
+	if (ext4_has_inline_data(inode))
+		return false;
+	return true;
+}
+
+static ssize_t ext4_dio_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	ssize_t ret;
+	struct inode *inode = file_inode(iocb->ki_filp);
+
+	/*
+	 * Get exclusion from truncate and other inode operations.
+	 */
+	if (!inode_trylock_shared(inode)) {
+		if (iocb->ki_flags & IOCB_NOWAIT)
+			return -EAGAIN;
+		inode_lock_shared(inode);
+	}
+
+	if (!ext4_dio_checks(inode)) {
+		inode_unlock_shared(inode);
+		/*
+		 * Fallback to buffered IO if the operation being
+		 * performed on the inode is not supported by direct
+		 * IO. The IOCB_DIRECT flag flags needs to be cleared
+		 * here to ensure that the direct IO code path within
+		 * generic_file_read_iter() is not taken again.
+		 */
+		iocb->ki_flags &= ~IOCB_DIRECT;
+		return generic_file_read_iter(iocb, to);
+	}
+
+	ret = iomap_dio_rw(iocb, to, &ext4_iomap_ops, NULL);
+	inode_unlock_shared(inode);
+
+	file_accessed(iocb->ki_filp);
+	return ret;
+}
+
 #ifdef CONFIG_FS_DAX
 static ssize_t ext4_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
 {
@@ -64,16 +111,19 @@  static ssize_t ext4_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
 
 static ssize_t ext4_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 {
-	if (unlikely(ext4_forced_shutdown(EXT4_SB(file_inode(iocb->ki_filp)->i_sb))))
+	struct inode *inode = file_inode(iocb->ki_filp);
+
+	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
 		return -EIO;
 
 	if (!iov_iter_count(to))
 		return 0; /* skip atime */
 
-#ifdef CONFIG_FS_DAX
-	if (IS_DAX(file_inode(iocb->ki_filp)))
+	if (IS_DAX(inode))
 		return ext4_dax_read_iter(iocb, to);
-#endif
+
+	if (iocb->ki_flags & IOCB_DIRECT)
+		return ext4_dio_read_iter(iocb, to);
 	return generic_file_read_iter(iocb, to);
 }