Re: [Ocfs2-devel] [PATCH 2/3] ocfs2: add ocfs2_overwrite_io function

[Changwei Ge]

Hi,
Gang

On 2017/11/27 17:48, Gang He wrote:
> Add ocfs2_overwrite_io function, which is used to judge if
> overwrite allocated blocks, otherwise, the write will bring extra
> block allocation overhead.
> 

Can you elaborate how this overhead is introduced?
Forgive me, I don't figure it.

Thanks,
Changwei

> Signed-off-by: Gang He <ghe@xxxxxxxx>
> ---
>   fs/ocfs2/extent_map.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++
>   fs/ocfs2/extent_map.h |  3 +++
>   2 files changed, 70 insertions(+)
> 
> diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
> index e4719e0..98bf325 100644
> --- a/fs/ocfs2/extent_map.c
> +++ b/fs/ocfs2/extent_map.c
> @@ -832,6 +832,73 @@ int ocfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>   	return ret;
>   }
>   
> +/* Is IO overwriting allocated blocks? */
> +int ocfs2_overwrite_io(struct inode *inode, u64 map_start, u64 map_len,
> +		       int wait)
> +{
> +	int ret = 0, is_last;
> +	u32 mapping_end, cpos;
> +	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
> +	struct buffer_head *di_bh = NULL;
> +	struct ocfs2_extent_rec rec;
> +
> +	if (wait)
> +		ret = ocfs2_inode_lock(inode, &di_bh, 0);
> +	else
> +		ret = ocfs2_try_inode_lock(inode, &di_bh, 0);
> +	if (ret)
> +		goto out;
> +
> +	if (wait)
> +		down_read(&OCFS2_I(inode)->ip_alloc_sem);
> +	else {
> +		if (!down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem)) {
> +			ret = -EAGAIN;
> +			goto out_unlock1;
> +		}
> +	}
> +
> +	if ((OCFS2_I(inode)->ip_dyn_features & OCFS2_INLINE_DATA_FL) &&
> +	   ((map_start + map_len) <= i_size_read(inode)))
> +		goto out_unlock2;
> +
> +	cpos = map_start >> osb->s_clustersize_bits;
> +	mapping_end = ocfs2_clusters_for_bytes(inode->i_sb,
> +					       map_start + map_len);
> +	is_last = 0;
> +	while (cpos < mapping_end && !is_last) {
> +		ret = ocfs2_get_clusters_nocache(inode, di_bh, cpos,
> +						 NULL, &rec, &is_last);
> +		if (ret) {
> +			mlog_errno(ret);
> +			goto out_unlock2;
> +		}
> +
> +		if (rec.e_blkno == 0ULL)
> +			break;
> +
> +		if (rec.e_flags & OCFS2_EXT_REFCOUNTED)
> +			break;
> +
> +		cpos = le32_to_cpu(rec.e_cpos) +
> +			le16_to_cpu(rec.e_leaf_clusters);
> +	}
> +
> +	if (cpos < mapping_end)
> +		ret = 1;
> +
> +out_unlock2:
> +	brelse(di_bh);
> +
> +	up_read(&OCFS2_I(inode)->ip_alloc_sem);
> +
> +out_unlock1:
> +	ocfs2_inode_unlock(inode, 0);
> +
> +out:
> +	return (ret ? 0 : 1);
> +}
> +
>   int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int whence)
>   {
>   	struct inode *inode = file->f_mapping->host;
> diff --git a/fs/ocfs2/extent_map.h b/fs/ocfs2/extent_map.h
> index 67ea57d..fd9e86a 100644
> --- a/fs/ocfs2/extent_map.h
> +++ b/fs/ocfs2/extent_map.h
> @@ -53,6 +53,9 @@ int ocfs2_extent_map_get_blocks(struct inode *inode, u64 v_blkno, u64 *p_blkno,
>   int ocfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>   		 u64 map_start, u64 map_len);
>   
> +int ocfs2_overwrite_io(struct inode *inode, u64 map_start, u64 map_len,
> +		       int wait);
> +
>   int ocfs2_seek_data_hole_offset(struct file *file, loff_t *offset, int origin);
>   
>   int ocfs2_xattr_get_clusters(struct inode *inode, u32 v_cluster,
>