On Tue, 9 Sep 2014 18:35:40 +0200, Andreas Rohner wrote:
> Under normal circumstances nilfs_sync_fs() writes out the super block,
> which causes a flush of the underlying block device. But this depends on
> the THE_NILFS_SB_DIRTY flag, which is only set if the pointer to the
> last segment crosses a segment boundary. So if only a small amount of
> data is written before the call to nilfs_sync_fs(), no flush of the
> block device occurs.
>
> In the above case an additional call to blkdev_issue_flush() is needed.
> To prevent unnecessary overhead, the new flag nilfs->ns_flushed_device
> is introduced, which is cleared whenever new logs are written and set
> whenever the block device is flushed.
>
> Signed-off-by: Andreas Rohner <andreas.rohner@xxxxxxx>
> ---
> fs/nilfs2/file.c | 6 +++++-
> fs/nilfs2/ioctl.c | 6 +++++-
> fs/nilfs2/segment.c | 4 ++++
> fs/nilfs2/super.c | 12 ++++++++++++
> fs/nilfs2/the_nilfs.c | 1 +
> fs/nilfs2/the_nilfs.h | 2 ++
> 6 files changed, 29 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nilfs2/file.c b/fs/nilfs2/file.c
> index 2497815..8a3e702 100644
> --- a/fs/nilfs2/file.c
> +++ b/fs/nilfs2/file.c
> @@ -56,7 +56,11 @@ int nilfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> mutex_unlock(&inode->i_mutex);
>
> nilfs = inode->i_sb->s_fs_info;
> - if (!err && nilfs_test_opt(nilfs, BARRIER)) {
> + if (!err && nilfs_test_opt(nilfs, BARRIER) &&
> + !atomic_read(&nilfs->ns_flushed_device)) {
> + atomic_set(&nilfs->ns_flushed_device, 1);
> + smp_mb__after_atomic();
> +
> err = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
> if (err != -EIO)
> err = 0;
> diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
> index 422fb54..47fe7cf 100644
> --- a/fs/nilfs2/ioctl.c
> +++ b/fs/nilfs2/ioctl.c
> @@ -1022,7 +1022,11 @@ static int nilfs_ioctl_sync(struct inode *inode, struct file *filp,
> return ret;
>
> nilfs = inode->i_sb->s_fs_info;
> - if (nilfs_test_opt(nilfs, BARRIER)) {
> + if (nilfs_test_opt(nilfs, BARRIER) &&
> + !atomic_read(&nilfs->ns_flushed_device)) {
> + atomic_set(&nilfs->ns_flushed_device, 1);
> + smp_mb__after_atomic();
> +
> ret = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
> if (ret == -EIO)
> return ret;
> diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
> index a1a1916..3119b64 100644
> --- a/fs/nilfs2/segment.c
> +++ b/fs/nilfs2/segment.c
> @@ -1997,6 +1997,10 @@ static int nilfs_segctor_do_construct(struct nilfs_sc_info *sci, int mode)
> err = nilfs_segctor_wait(sci);
> if (err)
> goto failed_to_write;
> +
> + if (test_bit(NILFS_SC_SUPER_ROOT, &sci->sc_flags) ||
> + mode == SC_LSEG_DSYNC)
> + atomic_set(&nilfs->ns_flushed_device, 0);
> }
> } while (sci->sc_stage.scnt != NILFS_ST_DONE);
>
> diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
> index 228f5bd..74a9930 100644
> --- a/fs/nilfs2/super.c
> +++ b/fs/nilfs2/super.c
> @@ -310,6 +310,8 @@ int nilfs_commit_super(struct super_block *sb, int flag)
> nilfs->ns_sbsize));
> }
> clear_nilfs_sb_dirty(nilfs);
> + atomic_set(&nilfs->ns_flushed_device, 1);
> + smp_mb__after_atomic();
> return nilfs_sync_super(sb, flag);
> }
>
> @@ -514,6 +516,16 @@ static int nilfs_sync_fs(struct super_block *sb, int wait)
> }
> up_write(&nilfs->ns_sem);
>
> + if (wait && !err && nilfs_test_opt(nilfs, BARRIER) &&
> + !atomic_read(&nilfs->ns_flushed_device)) {
> + atomic_set(&nilfs->ns_flushed_device, 1);
> + smp_mb__after_atomic();
> +
> + err = blkdev_issue_flush(sb->s_bdev, GFP_KERNEL, NULL);
> + if (err != -EIO)
> + err = 0;
> + }
> +
> return err;
> }
>
> diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
> index 9da25fe..d37c50b 100644
> --- a/fs/nilfs2/the_nilfs.c
> +++ b/fs/nilfs2/the_nilfs.c
> @@ -74,6 +74,7 @@ struct the_nilfs *alloc_nilfs(struct block_device *bdev)
> return NULL;
>
> nilfs->ns_bdev = bdev;
> + atomic_set(&nilfs->ns_flushed_device, 0);
> atomic_set(&nilfs->ns_ndirtyblks, 0);
> init_rwsem(&nilfs->ns_sem);
> mutex_init(&nilfs->ns_snapshot_mount_mutex);
> diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
> index d01ead1..ec53958 100644
> --- a/fs/nilfs2/the_nilfs.h
> +++ b/fs/nilfs2/the_nilfs.h
> @@ -45,6 +45,7 @@ enum {
>
> /**
> * struct the_nilfs - struct to supervise multiple nilfs mount points
> + * @ns_flushed_device: flag indicating if all volatile data was flushed
> * @ns_flags: flags
> * @ns_bdev: block device
> * @ns_sem: semaphore for shared states
> @@ -103,6 +104,7 @@ enum {
> */
> struct the_nilfs {
> unsigned long ns_flags;
> + atomic_t ns_flushed_device;
Andreas, can you implement this with just an integer variable like below ?
int ns_flushed_device
I want to limit the use of atomic_t type just for counters such as
ref-counts, statistics information, and so forth.
The load/store operations for this value is done atomically because
the_nilfs structure is natually aligned without "packed" attribute
though it may need that smp barriers are inserted properly.
> struct block_device *ns_bdev;
> struct rw_semaphore ns_sem;
> --
> 2.1.0
>
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