From: Liu Bo <bo.li.liu@oracle.com>
To: dsterba@suse.cz, linux-btrfs@vger.kernel.org, fdmanana@suse.com
Subject: Re: [RFC PATCH v2 2/2] Btrfs: improve fsync for nocow file
Date: Thu, 18 Jun 2015 11:27:24 +0800 [thread overview]
Message-ID: <20150618032722.GB8530@localhost.localdomain> (raw)
In-Reply-To: <20150617155836.GZ6761@twin.jikos.cz>
On Wed, Jun 17, 2015 at 05:58:36PM +0200, David Sterba wrote:
> On Wed, Jun 17, 2015 at 03:54:32PM +0800, Liu Bo 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: ~131Mb/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>
> > ---
> > v2: Catch errors from data writeback and skip barrier if necessary.
> >
> > fs/btrfs/btrfs_inode.h | 2 +
> > fs/btrfs/disk-io.c | 2 +-
> > fs/btrfs/disk-io.h | 1 +
> > fs/btrfs/file.c | 54 +++++++++++++++++++++++++++++++++++++++++++----
> > fs/btrfs/inode.c | 3 ++
> > 5 files changed, 56 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
> > index de5e4f2..f7b99b6 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
>
> It's not clear what the flags mean and that they're related to syncing
> under some conditions.
What do you think about BTRFS_ILOG_NOTIMESTAMP and BTRFS_ILOG_NOISIZE?
>
> > /*
> > * 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
> > --- 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_root *root,
> > u64 bytenr);
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index faa7d39..180a3e1 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -523,8 +523,12 @@ 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;
> > }
> >
> > @@ -1715,19 +1719,33 @@ 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,
> > @@ -1983,6 +2001,32 @@ 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)) {
> > +
> > + /* make sure data is on disk and catch error */
> > + if (!full_sync)
> > + ret = filemap_fdatawait_range(inode->i_mapping,
> > + start, end);
> > +
> > + if (!ret && !btrfs_test_opt(root, NOBARRIER)) {
> > + mutex_lock(&root->fs_info->
> > + fs_devices->device_list_mutex);
> > + ret = barrier_all_devices(root->fs_info);
>
> Calling barrier devices at this point looks very fishy, taking global
> device locks to sync one file as well. All files in the filesystem will
> pay the penalty for just one nodatacow file that's being synced.
Well, I'm afraid this is necessary as this is a fsync, an expensive operation,
in the normal case, each fsync issues a superblock flush which calls barrier devices.
I was expecting to not take the global device lock but btrfs is able to
manage multiple devices which requires us to do so.
>
> I'm not sure that handling the NOISIZE bit is safe regarding size
> extending and sync, ie. if it's properly synchronized with i_mutex from
> all contexts.
That's also my concern, but the worst case is that someone clears
NOISIZE bit and we continue on the normal fsync path.
And this NOISIZE bit not only stands for i_size change, but also will be
cleared when we do COW, I'm not sure if we need to use another bit for
the COW change or not.
Thanks,
-liubo
>
> > + if (ret)
> > + btrfs_error(root->fs_info, ret,
> > + "errors while submitting device barriers.");
> > + mutex_unlock(&root->fs_info->
> > + fs_devices->device_list_mutex);
> > + }
> > + mutex_unlock(&inode->i_mutex);
> > + goto out;
> > + }
> > + }
>
>
> > +
> > /*
> > * 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 43192e1..e2912c8 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -1383,6 +1383,7 @@ 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);
> > @@ -1425,6 +1426,7 @@ 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;
> > }
> > @@ -1463,6 +1465,7 @@ 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)
> > --
> > 1.7.7.6
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
next prev parent reply other threads:[~2015-06-18 3:27 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-17 7:54 [RFC PATCH v2 1/2] Btrfs: add noi_version option to disable MS_I_VERSION Liu Bo
2015-06-17 7:54 ` [RFC PATCH v2 2/2] Btrfs: improve fsync for nocow file Liu Bo
2015-06-17 15:58 ` David Sterba
2015-06-18 3:27 ` Liu Bo [this message]
2015-06-24 18:21 ` David Sterba
2015-06-25 2:24 ` Liu Bo
2015-06-25 16:10 ` David Sterba
2015-06-17 15:33 ` [RFC PATCH v2 1/2] Btrfs: add noi_version option to disable MS_I_VERSION David Sterba
2015-06-17 15:52 ` Liu Bo
2015-06-17 17:01 ` David Sterba
2015-06-18 2:46 ` Liu Bo
2015-06-18 14:38 ` i_version vs iversion (Was: Re: [RFC PATCH v2 1/2] Btrfs: add noi_version option to disable MS_I_VERSION) David Sterba
2015-06-19 11:44 ` Karel Zak
2015-06-19 11:44 ` Karel Zak
2015-06-22 20:42 ` Dave Chinner
2015-06-22 20:42 ` Dave Chinner
2015-06-24 17:28 ` David Sterba
2015-06-23 16:32 ` Theodore Ts'o
2015-06-24 8:23 ` Liu Bo
2015-06-24 18:02 ` David Sterba
2015-06-24 23:17 ` Theodore Ts'o
2015-06-24 23:17 ` Theodore Ts'o
2015-06-24 23:59 ` Dave Chinner
2015-06-24 23:59 ` Dave Chinner
2015-06-25 18:46 ` J. Bruce Fields
2015-06-25 18:46 ` J. Bruce Fields
2015-06-25 22:12 ` Theodore Ts'o
2015-06-26 13:32 ` J. Bruce Fields
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