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

[Changwei Ge]

On 2017/11/28 9:52, piaojun wrote:
> Hi Gang,
> 
> If ocfs2_overwrite_io is only called in 'nowait' scenarios, I wonder if
> we can discard 'int wait' just as ext4 does:
> 
> static bool ext4_overwrite_io(struct inode *inode, loff_t pos, loff_t len);

Yes, Jun has a point.
It seems that ocfs2_overwrite_io is only involved in non-blocking aio 
and no other code spot is calling ocfs2_overwrite_io with wait=1 passed.

> 
> thans,
> Jun
> 
> On 2017/11/27 17:46, 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.
>>
>> 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;
Here is a little strange, it seems that you don't care much about how 
this function fails. Why evaluate _ret_ to  -EAGAIN here and ignore it 
later?

Thanks,
Changwei

>> +			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,
>>
> 
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