[1/5] ext4: introduce direct IO read code path using iomap infrastructure
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Message ID 3e83a70c4442c6aeb15b7913c39f853e7386a3c3.1565609891.git.mbobrowski@mbobrowski.org
State New
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Series
  • ext4: direct IO via iomap infrastructure
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Commit Message

Matthew Bobrowski Aug. 12, 2019, 12:52 p.m. UTC
This patch introduces a new direct IO read code path implementation
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 try to take that path. Prior to doing so, we drop the
IOCB_DIRECT flag from iocb->ki_flags to prevent generic_file_read_iter() from
taking the direct IO code path once again.

Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
---
 fs/ext4/file.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 53 insertions(+), 2 deletions(-)

Comments

Christoph Hellwig Aug. 12, 2019, 5:18 p.m. UTC | #1
On Mon, Aug 12, 2019 at 10:52:35PM +1000, Matthew Bobrowski wrote:
> +#ifdef CONFIG_FS_ENCRYPTION
> +	if (IS_ENCRYPTED(inode))
> +		return false;
> +#endif

This could use IS_ENABLED.

>  		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

Same here.
Matthew Wilcox Aug. 12, 2019, 8:17 p.m. UTC | #2
On Mon, Aug 12, 2019 at 10:18:35AM -0700, Christoph Hellwig wrote:
> >  		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
> 
> Same here.

It doesn't even need IS_ENABLED.

include/linux/fs.h:#define IS_DAX(inode)                ((inode)->i_flags & S_DAX)

#ifdef CONFIG_FS_DAX
#define S_DAX           8192    /* Direct Access, avoiding the page cache */
#else
#define S_DAX           0       /* Make all the DAX code disappear */
#endif
Matthew Bobrowski Aug. 13, 2019, 10:45 a.m. UTC | #3
On Mon, Aug 12, 2019 at 01:17:35PM -0700, Matthew Wilcox wrote:
> On Mon, Aug 12, 2019 at 10:18:35AM -0700, Christoph Hellwig wrote:
> > >  		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
> > 
> > Same here.
> 
> It doesn't even need IS_ENABLED.
> 
> include/linux/fs.h:#define IS_DAX(inode)                ((inode)->i_flags & S_DAX)
> 
> #ifdef CONFIG_FS_DAX
> #define S_DAX           8192    /* Direct Access, avoiding the page cache */
> #else
> #define S_DAX           0       /* Make all the DAX code disappear */
> #endif

Ah, clever - I like it! I actually didn't see this and thank you for
highlighting. I guess I will be dropping the CONFIG_FS_DAX statement
here...

--M

Patch
diff mbox series

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 70b0438dbc94..360eff7b6aa2 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)
+{
+#ifdef 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 from iocb->ki_flags needs
+		 * to be cleared here to ensure that the direct IO
+		 * code path in generic_file_read_iter() is not taken.
+		 */
+		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 +111,20 @@  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);
 }