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

[Changwei Ge]

On 2017/11/28 13:44, Gang He wrote:
> Hi Changwei,
> 
> 
>>>>
>> 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.
> If the blocks have been allocated, we just write these block directly.
> If these blocks have not been allocated, that means we need to allocate these block firstly before write,
> this allocation will bring the IO invoking be blocked, if the upper application does not want take this kind of overhead,
> he can pass a nowait flag to avoid and return immediately with a -EAGAIN error.

Thanks for your answer and contribution.
This makes sense.

Changwei

> 
> Thanks
> Gang
> 
>>
>> 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,
>>>
> 
>