[Ocfs2-devel] [PATCH] ocfs2: reflink: fix slow unlink for refcounted file

[Wengang <wen.gang.wang@oracle.com>]

Will it be safe to do the moving?

There are three calls of ocfs2_remove_btree_range

1 7124 fs/ocfs2/alloc.c <<ocfs2_commit_truncate>>
status = ocfs2_remove_btree_range(inode, &et, trunc_cpos,
2 4479 fs/ocfs2/dir.c <<ocfs2_dx_dir_truncate>>
ret = ocfs2_remove_btree_range(dir, &et, cpos, p_cpos, clen, 0,
3 1805 fs/ocfs2/file.c <<ocfs2_remove_inode_range>>
ret = ocfs2_remove_btree_range(inode, &et, trunc_cpos,

Obviously, the 2nd and the 3rd are not sub-routines of 
ocfs2_commit_truncate().

I think this moving is not safe.

thanks,
wengang

? 2014?07?25? 13:32, Junxiao Bi ??:
> When running ocfs2 test suite multiple nodes reflink stress test, for
> a 4 nodes cluster, every unlink() for refcounted file needs about 700s.
>
> The slow unlink is caused by the contention of refcount tree lock since all
> nodes are unlink files using the same refcount tree. When the unlinking file
> have many extents(over 1600 in our test), most of the extents has refcounted
> flag set. In ocfs2_commit_truncate(), it will execute the following call trace
> for every extents. This means it needs get and released refcount tree lock
> about 1600 times. And when several nodes are do this at the same time, the
> performance will be very low.
> .
> ocfs2_remove_btree_range()
> ----ocfs2_lock_refcount_tree()
> ------ocfs2_refcount_lock()
> --------__ocfs2_cluster_lock()
>
> ocfs2_refcount_lock() is costly, move it to ocfs2_commit_truncate() to do
> lock/unlock once can improve a lot performance.
>
> Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
> ---
>   fs/ocfs2/alloc.c |   22 ++++++++++++----------
>   1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
> index 9d8fcf2..a764363 100644
> --- a/fs/ocfs2/alloc.c
> +++ b/fs/ocfs2/alloc.c
> @@ -5667,13 +5667,6 @@ int ocfs2_remove_btree_range(struct inode *inode,
>   		BUG_ON(!(OCFS2_I(inode)->ip_dyn_features &
>   			 OCFS2_HAS_REFCOUNT_FL));
>   
> -		ret = ocfs2_lock_refcount_tree(osb, refcount_loc, 1,
> -					       &ref_tree, NULL);
> -		if (ret) {
> -			mlog_errno(ret);
> -			goto bail;
> -		}
> -
>   		ret = ocfs2_prepare_refcount_change_for_del(inode,
>   							    refcount_loc,
>   							    phys_blkno,
> @@ -5755,9 +5748,6 @@ bail:
>   	if (meta_ac)
>   		ocfs2_free_alloc_context(meta_ac);
>   
> -	if (ref_tree)
> -		ocfs2_unlock_refcount_tree(osb, ref_tree, 1);
> -
>   	return ret;
>   }
>   
> @@ -7012,6 +7002,7 @@ int ocfs2_commit_truncate(struct ocfs2_super *osb,
>   	u64 refcount_loc = le64_to_cpu(di->i_refcount_loc);
>   	struct ocfs2_extent_tree et;
>   	struct ocfs2_cached_dealloc_ctxt dealloc;
> +	struct ocfs2_refcount_tree *ref_tree = NULL;
>   
>   	ocfs2_init_dinode_extent_tree(&et, INODE_CACHE(inode), di_bh);
>   	ocfs2_init_dealloc_ctxt(&dealloc);
> @@ -7121,6 +7112,15 @@ start:
>   
>   	phys_cpos = ocfs2_blocks_to_clusters(inode->i_sb, blkno);
>   
> +	if ((flags & OCFS2_EXT_REFCOUNTED) && trunc_len && !ref_tree) {
> +		status = ocfs2_lock_refcount_tree(osb, refcount_loc, 1,
> +				&ref_tree, NULL);
> +		if (status) {
> +			mlog_errno(status);
> +			goto bail;
> +		}
> +	}
> +
>   	status = ocfs2_remove_btree_range(inode, &et, trunc_cpos,
>   					  phys_cpos, trunc_len, flags, &dealloc,
>   					  refcount_loc);
> @@ -7138,6 +7138,8 @@ start:
>   	goto start;
>   
>   bail:
> +	if (ref_tree)
> +		ocfs2_unlock_refcount_tree(osb, ref_tree, 1);
>   
>   	ocfs2_schedule_truncate_log_flush(osb, 1);
>