Re: [RFC PATCH 2/2] Btrfs: improve fsync for nocow file

[Liu Bo <bo.li.liu@oracle.com>]

On Tue, Jun 09, 2015 at 01:56:41PM +0100, Filipe David Manana wrote:
> On Tue, Jun 9, 2015 at 1:04 PM, Liu Bo <bo.li.liu@oracle.com> wrote:
> > If  we're overwriting an allocated file without changing timestamp
> > and inode version, and the file is with NODATACOW, we don't have any metadata to
> > commit, thus we can just flush the data device cache and go forward.
> >
> > However, if there's have any change on extents' disk bytenr, inode size,
> > timestamp or inode version, we need to go through the normal btrfs_log_inode
> > path.
> >
> > Test:
> > ----------------------------
> > 1. sysbench test of
> > "1 file + 1 thread + bs=4k + size=40k + synchronous I/O mode + randomwrite +
> > fsync_on_each_write",
> > 2. loop device associated with tmpfs file
> > 3.
> >   - For btrfs, "-o nodatacow" and "-o noi_version" option
> >   - For ext4 and xfs, no extra mount options
> > ----------------------------
> >
> > Results:
> > ----------------------------
> > - btrfs:
> > w/o: ~30Mb/sec
> > w:   ~181Mb/sec
> >
> > - other filesystems: (both don't enable i_version by default)
> > ext4:  203Mb/sec
> > xfs:   212Mb/sec
> > ----------------------------
> >
> > Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> > ---
> >  fs/btrfs/btrfs_inode.h |  2 ++
> >  fs/btrfs/disk-io.c     |  2 +-
> >  fs/btrfs/disk-io.h     |  1 +
> >  fs/btrfs/file.c        | 39 ++++++++++++++++++++++++++++++++++-----
> >  fs/btrfs/inode.c       |  3 +++
> >  5 files changed, 41 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
> > index 0ef5cc1..b36d87a 100644
> > --- a/fs/btrfs/btrfs_inode.h
> > +++ b/fs/btrfs/btrfs_inode.h
> > @@ -44,6 +44,8 @@
> >  #define BTRFS_INODE_IN_DELALLOC_LIST           9
> >  #define BTRFS_INODE_READDIO_NEED_LOCK          10
> >  #define BTRFS_INODE_HAS_PROPS                  11
> > +#define BTRFS_INODE_NOTIMESTAMP                        12
> > +#define BTRFS_INODE_NOISIZE                    13
> >  /*
> >   * The following 3 bits are meant only for the btree inode.
> >   * When any of them is set, it means an error happened while writing an
> > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> > index 2ef9a4b..de7fd94 100644
> > --- a/fs/btrfs/disk-io.c
> > +++ b/fs/btrfs/disk-io.c
> > @@ -3343,7 +3343,7 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
> >   * send an empty flush down to each device in parallel,
> >   * then wait for them
> >   */
> > -static int barrier_all_devices(struct btrfs_fs_info *info)
> > +int barrier_all_devices(struct btrfs_fs_info *info)
> >  {
> >         struct list_head *head;
> >         struct btrfs_device *dev;
> > diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
> > index d4cbfee..2bc91fe 100644
> > --- a/fs/btrfs/disk-io.h
> > +++ b/fs/btrfs/disk-io.h
> > @@ -60,6 +60,7 @@ void close_ctree(struct btrfs_root *root);
> >  int write_ctree_super(struct btrfs_trans_handle *trans,
> >                       struct btrfs_root *root, int max_mirrors);
> >  struct buffer_head *btrfs_read_dev_super(struct block_device *bdev);
> > +int barrier_all_devices(struct btrfs_fs_info *info);
> >  int btrfs_commit_super(struct btrfs_root *root);
> >  struct extent_buffer *btrfs_find_tree_block(struct btrfs_fs_info *fs_info,
> >                                             u64 bytenr);
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index 23b6e03..861c29f 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -519,8 +519,12 @@ int btrfs_dirty_pages(struct btrfs_root *root, struct inode *inode,
> >          * the disk i_size.  There is no need to log the inode
> >          * at this time.
> >          */
> > -       if (end_pos > isize)
> > +       if (end_pos > isize) {
> >                 i_size_write(inode, end_pos);
> > +               clear_bit(BTRFS_INODE_NOISIZE, &BTRFS_I(inode)->runtime_flags);
> > +       } else {
> > +               set_bit(BTRFS_INODE_NOISIZE, &BTRFS_I(inode)->runtime_flags);
> > +       }
> >         return 0;
> >  }
> >
> > @@ -1711,19 +1715,33 @@ out:
> >  static void update_time_for_write(struct inode *inode)
> >  {
> >         struct timespec now;
> > +       int sync_it = 0;
> >
> > -       if (IS_NOCMTIME(inode))
> > +       if (IS_NOCMTIME(inode)) {
> > +               set_bit(BTRFS_INODE_NOTIMESTAMP, &BTRFS_I(inode)->runtime_flags);
> >                 return;
> > +       }
> >
> >         now = current_fs_time(inode->i_sb);
> > -       if (!timespec_equal(&inode->i_mtime, &now))
> > +       if (!timespec_equal(&inode->i_mtime, &now)) {
> >                 inode->i_mtime = now;
> > +               sync_it = S_MTIME;
> > +       }
> >
> > -       if (!timespec_equal(&inode->i_ctime, &now))
> > +       if (!timespec_equal(&inode->i_ctime, &now)) {
> >                 inode->i_ctime = now;
> > +               sync_it |= S_CTIME;
> > +       }
> >
> > -       if (IS_I_VERSION(inode))
> > +       if (IS_I_VERSION(inode)) {
> >                 inode_inc_iversion(inode);
> > +               sync_it |= S_VERSION;
> > +       }
> > +
> > +       if (!sync_it)
> > +               set_bit(BTRFS_INODE_NOTIMESTAMP, &BTRFS_I(inode)->runtime_flags);
> > +       else
> > +               clear_bit(BTRFS_INODE_NOTIMESTAMP, &BTRFS_I(inode)->runtime_flags);
> >  }
> >
> >  static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> > @@ -1987,6 +2005,17 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> >                 goto out;
> >         }
> >
> > +       if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW) {
> > +               if (test_and_clear_bit(BTRFS_INODE_NOTIMESTAMP,
> > +                                       &BTRFS_I(inode)->runtime_flags) &&
> > +                   test_and_clear_bit(BTRFS_INODE_NOISIZE,
> > +                                       &BTRFS_I(inode)->runtime_flags)) {
> > +                       barrier_all_devices(root->fs_info);
> > +                       mutex_unlock(&inode->i_mutex);
> > +                       goto out;
> 
> Hi Liu,
> 
> For the non-full sync case, what happens if an IO error happened
> during writeback?
> I don't see anything here that checks if an IO error happened and
> return -EIO to user space if such error happened.
> In other words, testing for the bit AS_EIO in the inode->i_mapping->flags.

Good point, I missed that part.

Besides that, is the whole "noi_version and nocow" idea acceptable to you?

Thanks,

-liubo

> 
> thanks
> 
> > +               }
> > +       }
> > +
> >         /*
> >          * ok we haven't committed the transaction yet, lets do a commit
> >          */
> > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > index 0020b56..3d230e6 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -1384,6 +1384,7 @@ out_check:
> >
> >                 btrfs_release_path(path);
> >                 if (cow_start != (u64)-1) {
> > +                       clear_bit(BTRFS_INODE_NOISIZE, &BTRFS_I(inode)->runtime_flags);
> >                         ret = cow_file_range(inode, locked_page,
> >                                              cow_start, found_key.offset - 1,
> >                                              page_started, nr_written, 1);
> > @@ -1426,6 +1427,7 @@ out_check:
> >                                                 em->start + em->len - 1, 0);
> >                         }
> >                         type = BTRFS_ORDERED_PREALLOC;
> > +                       clear_bit(BTRFS_INODE_NOISIZE, &BTRFS_I(inode)->runtime_flags);
> >                 } else {
> >                         type = BTRFS_ORDERED_NOCOW;
> >                 }
> > @@ -1464,6 +1466,7 @@ out_check:
> >         }
> >
> >         if (cow_start != (u64)-1) {
> > +               clear_bit(BTRFS_INODE_NOISIZE, &BTRFS_I(inode)->runtime_flags);
> >                 ret = cow_file_range(inode, locked_page, cow_start, end,
> >                                      page_started, nr_written, 1);
> >                 if (ret)
> > --
> > 2.1.0
> >
> > --
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> 
> 
> 
> -- 
> Filipe David Manana,
> 
> "Reasonable men adapt themselves to the world.
>  Unreasonable men adapt the world to themselves.
>  That's why all progress depends on unreasonable men."