[PATCH 8/8] xfs: add initial DAX support

Dave Chinner
2015-03-24T10:51:26Z

From: Dave Chinner <dchinner@redhat.com>

Add initial DAX support to XFS. To do this we need a new mount
option to turn DAX on filesystem, and we need to propagate thi into
the inode flags whenever an inode is instantiated so that the
per-inode checks throughout the code Do The Right Thing.

There are still some things remaining to be done:

- needs per-inode flags to mark inodes as DAX enabled, and
an inheritance flag to enable automatic filesystem
propagation of the property
- fails occasionally with zero length writes instead of
ENOSPC errors, so error propagation inside/from the DAX
code need work
- occasionally creates two extents rather than a single
larger extent like non-dax filesystems.
- much more testing

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/xfs_iops.c | 24 ++++++++++++------------
fs/xfs/xfs_mount.h | 2 ++
fs/xfs/xfs_super.c | 25 +++++++++++++++++++++++--
3 files changed, 37 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 9ca5352..695d857 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -1195,22 +1195,22 @@ xfs_diflags_to_iflags(
struct inode *inode,
struct xfs_inode *ip)
{
- if (ip->i_d.di_flags & XFS_DIFLAG_IMMUTABLE)
+ uint16_t flags = ip->i_d.di_flags;
+
+ inode->i_flags &= ~(S_IMMUTABLE | S_APPEND | S_SYNC |
+ S_NOATIME | S_DAX);
+
+ if (flags & XFS_DIFLAG_IMMUTABLE)
inode->i_flags |= S_IMMUTABLE;
- else
- inode->i_flags &= ~S_IMMUTABLE;
- if (ip->i_d.di_flags & XFS_DIFLAG_APPEND)
+ if (flags & XFS_DIFLAG_APPEND)
inode->i_flags |= S_APPEND;
- else
- inode->i_flags &= ~S_APPEND;
- if (ip->i_d.di_flags & XFS_DIFLAG_SYNC)
+ if (flags & XFS_DIFLAG_SYNC)
inode->i_flags |= S_SYNC;
- else
- inode->i_flags &= ~S_SYNC;
- if (ip->i_d.di_flags & XFS_DIFLAG_NOATIME)
+ if (flags & XFS_DIFLAG_NOATIME)
inode->i_flags |= S_NOATIME;
- else
- inode->i_flags &= ~S_NOATIME;
+ /* XXX: Also needs an on-disk per inode flag! */
+ if (ip->i_mount->m_flags & XFS_MOUNT_DAX)
+ inode->i_flags |= S_DAX;
}

/*
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 8c995a2..cd44e88 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -179,6 +179,8 @@ typedef struct xfs_mount {
allocator */
#define XFS_MOUNT_NOATTR2 (1ULL << 25) /* disable use of attr2 format */

+#define XFS_MOUNT_DAX (1ULL << 62) /* TEST ONLY! */
+

/*
* Default minimum read and write sizes.
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 3ad0b17..0f26d7a 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -112,6 +112,8 @@ static struct xfs_kobj xfs_dbg_kobj; /* global debug sysfs attrs */
#define MNTOPT_DISCARD "discard" /* Discard unused blocks */
#define MNTOPT_NODISCARD "nodiscard" /* Do not discard unused blocks */

+#define MNTOPT_DAX "dax" /* Enable direct access to bdev pages */
+
/*
* Table driven mount option parser.
*
@@ -363,6 +365,10 @@ xfs_parseargs(
mp->m_flags |= XFS_MOUNT_DISCARD;
} else if (!strcmp(this_char, MNTOPT_NODISCARD)) {
mp->m_flags &= ~XFS_MOUNT_DISCARD;
+#ifdef CONFIG_FS_DAX
+ } else if (!strcmp(this_char, MNTOPT_DAX)) {
+ mp->m_flags |= XFS_MOUNT_DAX;
+#endif
} else {
xfs_warn(mp, "unknown mount option [%s].", this_char);
return -EINVAL;
@@ -452,8 +458,8 @@ done:
}

struct proc_xfs_info {
- int flag;
- char *str;
+ uint64_t flag;
+ char *str;
};

STATIC int
@@ -474,6 +480,7 @@ xfs_showargs(
{ XFS_MOUNT_GRPID, "," MNTOPT_GRPID },
{ XFS_MOUNT_DISCARD, "," MNTOPT_DISCARD },
{ XFS_MOUNT_SMALL_INUMS, "," MNTOPT_32BITINODE },
+ { XFS_MOUNT_DAX, "," MNTOPT_DAX },
{ 0, NULL }
};
static struct proc_xfs_info xfs_info_unset[] = {
@@ -1501,6 +1508,20 @@ xfs_fs_fill_super(
if (XFS_SB_VERSION_NUM(&mp->m_sb) == XFS_SB_VERSION_5)
sb->s_flags |= MS_I_VERSION;

+ if (mp->m_flags & XFS_MOUNT_DAX) {
+ xfs_warn(mp,
+ "DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
+ if (sb->s_blocksize != PAGE_SIZE) {
+ xfs_alert(mp,
+ "Filesystem block size invalid for DAX Turning DAX off.");
+ mp->m_flags &= ~XFS_MOUNT_DAX;
+ } else if (!sb->s_bdev->bd_disk->fops->direct_access) {
+ xfs_alert(mp,
+ "Block device does not support DAX Turning DAX off.");
+ mp->m_flags &= ~XFS_MOUNT_DAX;
+ }
+ }
+
error = xfs_mountfs(mp);
if (error)
goto out_filestream_unmount;
--
2.0.0