On Tue, 9 Sep 2014 23:17:09 +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 | 10 +++++++++-
> fs/nilfs2/ioctl.c | 10 +++++++++-
> fs/nilfs2/segment.c | 4 ++++
> fs/nilfs2/super.c | 17 +++++++++++++++++
> fs/nilfs2/the_nilfs.h | 2 ++
> 5 files changed, 41 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nilfs2/file.c b/fs/nilfs2/file.c
> index 2497815..16375c2 100644
> --- a/fs/nilfs2/file.c
> +++ b/fs/nilfs2/file.c
> @@ -56,7 +56,15 @@ 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) &&
> + !nilfs->ns_flushed_device) {
> + nilfs->ns_flushed_device = 1;
> + /*
> + * the store to ns_flushed_device must not be reordered after
> + * blkdev_issue_flush
> + */
> + smp_wmb();
> +
> err = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
> if (err != -EIO)
> err = 0;
Looks good. But, these code lines and the comment appear repeatedly.
To simplify these, I propose to add the following inline function to
the_nilfs.h.
@@ -371,4 +373,24 @@ static inline int nilfs_segment_is_active(struct the_nilfs *nilfs, __u64 n)
return n == nilfs->ns_segnum || n == nilfs->ns_nextnum;
}
+static inline int nilfs_flush_device(struct the_nilfs *nilfs)
+{
+ int err;
+
+ if (!nilfs_test_opt(nilfs, BARRIER) || nilfs->ns_flushed_device)
+ return 0;
+
+ nilfs->ns_flushed_device = 1;
+ /*
+ * the store to ns_flushed_device must not be reordered after
+ * blkdev_issue_flush().
+ */
+ smp_wmb();
+
+ err = blkdev_issue_flush(nilfs->ns_bdev, GFP_KERNEL, NULL);
+ if (err != -EIO)
+ err = 0;
+ return err;
+}
+
#endif /* _THE_NILFS_H */
> diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
> index 422fb54..9444d5d 100644
> --- a/fs/nilfs2/ioctl.c
> +++ b/fs/nilfs2/ioctl.c
> @@ -1022,7 +1022,15 @@ 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) &&
> + !nilfs->ns_flushed_device) {
> + nilfs->ns_flushed_device = 1;
> + /*
> + * the store to ns_flushed_device must not be reordered after
> + * blkdev_issue_flush
> + */
> + smp_wmb();
> +
> 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..379da1b 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)
> + nilfs->ns_flushed_device = 0;
> }
> } while (sci->sc_stage.scnt != NILFS_ST_DONE);
We can simplify this by inserting "nilfs->ns_flushed_device = 0" in
nilfs_segctor_complete_write() and nilfs_construct_dsync_segment()
separately as follows. Explicit memory barriers are not required in
the following changes because both nilfs_set_last_segment() and
nilfs_transaction_unlock() imply a memory barrier.
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1833,6 +1833,7 @@ static void nilfs_segctor_complete_write(struct nilfs_sc_info *sci)
nilfs_set_next_segment(nilfs, segbuf);
if (update_sr) {
+ nilfs->ns_flushed_device = 0;
nilfs_set_last_segment(nilfs, segbuf->sb_pseg_start,
segbuf->sb_sum.seg_seq, nilfs->ns_cno++);
@@ -2216,6 +2217,8 @@ int nilfs_construct_dsync_segment(struct super_block *sb, struct inode *inode,
sci->sc_dsync_end = end;
err = nilfs_segctor_do_construct(sci, SC_LSEG_DSYNC);
+ if (!err)
+ nilfs->ns_flushed_device = 0;
nilfs_transaction_unlock(sb);
return err;
> diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
> index 228f5bd..33aafbd 100644
> --- a/fs/nilfs2/super.c
> +++ b/fs/nilfs2/super.c
> @@ -310,6 +310,9 @@ int nilfs_commit_super(struct super_block *sb, int flag)
> nilfs->ns_sbsize));
> }
> clear_nilfs_sb_dirty(nilfs);
> + nilfs->ns_flushed_device = 1;
> + /* make sure store to ns_flushed_device cannot be reordered */
> + smp_wmb();
> return nilfs_sync_super(sb, flag);
> }
>
> @@ -514,6 +517,20 @@ static int nilfs_sync_fs(struct super_block *sb, int wait)
> }
> up_write(&nilfs->ns_sem);
>
> + if (wait && !err && nilfs_test_opt(nilfs, BARRIER) &&
> + !nilfs->ns_flushed_device) {
> + nilfs->ns_flushed_device = 1;
> + /*
> + * the store to ns_flushed_device must not be reordered after
> + * blkdev_issue_flush
> + */
> + smp_wmb();
> +
> + err = blkdev_issue_flush(sb->s_bdev, GFP_KERNEL, NULL);
> + if (err != -EIO)
> + err = 0;
> + }
> +
> return err;
> }
>
> diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
> index d01ead1..dabb02c 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_flushed_device is inserted after ns_flags, so these two comment lines
should be swapped.
> * @ns_bdev: block device
> * @ns_sem: semaphore for shared states
> @@ -103,6 +104,7 @@ enum {
> */
> struct the_nilfs {
> unsigned long ns_flags;
> + int ns_flushed_device;
>
> struct block_device *ns_bdev;
> struct rw_semaphore ns_sem;
> --
> 2.1.0
Regards,
Ryusuke Konishi
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