Re: [PATCH] Btrfs: avoid heavy operations in btrfs_commit_super

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

On Mon, Nov 04, 2013 at 09:49:59AM +0100, Stefan Behrens wrote:
> On Sun,  3 Nov 2013 23:24:34 +0800, Liu Bo wrote:
> > The 'git blame' history shows that, the old transaction commit code has to do
> > twice to ensure roots are updated and we have to flush metadata and super block
> > manually, however, right now all of these can be handled well inside
> > the transaction commit code without extra efforts.
> > 
> > And the error handling part remains same with the current code, -- 'return to
> > caller once we get error'.
> > 
> > This saves us a transaction commit and a flush of super block, which are both
> > heavy operations according to ftrace output analysis.
> > 
> > Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> > ---
> >  fs/btrfs/disk-io.c | 20 +-------------------
> >  1 file changed, 1 insertion(+), 19 deletions(-)
> > 
> > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> > index 62176ad..d6728c3 100644
> > --- a/fs/btrfs/disk-io.c
> > +++ b/fs/btrfs/disk-io.c
> > @@ -3542,25 +3542,7 @@ int btrfs_commit_super(struct btrfs_root *root)
> >  	trans = btrfs_join_transaction(root);
> >  	if (IS_ERR(trans))
> >  		return PTR_ERR(trans);
> > -	ret = btrfs_commit_transaction(trans, root);
> > -	if (ret)
> > -		return ret;
> > -	/* run commit again to drop the original snapshot */
> > -	trans = btrfs_join_transaction(root);
> > -	if (IS_ERR(trans))
> > -		return PTR_ERR(trans);
> > -	ret = btrfs_commit_transaction(trans, root);
> > -	if (ret)
> > -		return ret;
> > -	ret = btrfs_write_and_wait_transaction(NULL, root);
> > -	if (ret) {
> > -		btrfs_error(root->fs_info, ret,
> > -			    "Failed to sync btree inode to disk.");
> > -		return ret;
> > -	}
> > -
> > -	ret = write_ctree_super(NULL, root, 0);
> > -	return ret;
> > +	return btrfs_commit_transaction(trans, root);
> >  }
> >  
> >  int close_ctree(struct btrfs_root *root)
> > 
> 
> fs/btrfs/disk-io.c: In function 'btrfs_commit_super':
> fs/btrfs/disk-io.c:3520: warning: unused variable 'ret'
> 

Oops, sorry for that, will fix it soon.

thanks,
-liubo