[Ocfs2-devel] [PATCH v2] ocfs2: fall back to buffer IO when append dio is disabled with file hole existing

[Junxiao Bi]

Hi Changwei,

On 12/26/2017 05:20 PM, Changwei Ge wrote:
> Hi Alex
> 
> On 2017/12/26 16:20, alex chen wrote:
>> Hi Changwei,
>>
>> On 2017/12/26 15:03, Changwei Ge wrote:
>>> The intention of this patch is to provide an option to ocfs2 users whether
>>> to allocate disk space while doing dio write.
>>>
>>> Whether to make ocfs2 fall back to buffer io is up to ocfs2 users through
>>> toggling append-dio feature. It rather makes ocfs2 configurable and
>>> flexible.
>>>
>> It is too strange to make ocfs2 fall back to buffer io by toggling append-dio feature.
> 
> It might be.
> But as my changelog said, I think, append-dio is key to whether to allocate
> space with dio writing. So filling hole and appending file should have the same reflection.
> 
> Besides, in the early days, ocfs2 truly falls back to buffer io when append-dio is disabled and file hole is encountered.
I think we have discussed a lot in your v1 version. This wasn't fit for
mainline, you can keep one off-mainline patch.

Thanks,
Junxiao.

> 
> Thanks,
> Changwei
> 
>>
>>> So if something bad happens to dio write with space allocation, we can
>>> still make ocfs2 fall back to buffer io. It's an option not a mandatory
>>> action.:)
>> Now the ocfs2 supports fill holes during direct io whether or not supporting append-dio feature
>> and we can directly fix the problem.
>> I think it is meaningless to provide an temporary option to turn off it.
> 
> IMO, this patch is NOT a temporary solution.
> Instead, it provides an extra option to ocfs2 users. And append-dio is enabled while making fs by *default*.
> 
> Thanks,
> Changwei  
> 
>>
>>>
>>> Besides, append-dio feature is key to whether to allocate space with dio
>>> writing. So writing to file hole and enlarging file(appending file) should
>>> have the same reflection to append-dio feature.
>>>
>>> Signed-off-by: Changwei Ge <ge.changwei at h3c.com>
>>> ---
>>>    fs/ocfs2/aops.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++---
>>>    1 file changed, 50 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
>>> index d151632..32e60c0 100644
>>> --- a/fs/ocfs2/aops.c
>>> +++ b/fs/ocfs2/aops.c
>>> @@ -2414,12 +2414,52 @@ static int ocfs2_dio_end_io(struct kiocb *iocb,
>>>    	return ret;
>>>    }
>>>    
>>> +/*
>>> + * Will look for holes and unwritten extents in the range starting at
>>> + * pos for count bytes (inclusive).
>>> + * Return value 1 indicates hole exists, 0 not exists, others indicate error.
>>> + */
>>> +static int ocfs2_range_has_holes(struct inode *inode, loff_t pos,
>>> +				 size_t count)
>>> +{
>>> +	int ret = 0;
>>> +	unsigned int extent_flags;
>>> +	u32 cpos, clusters, extent_len, phys_cpos;
>>> +	struct super_block *sb = inode->i_sb;
>>> +
>>> +	cpos = pos >> OCFS2_SB(sb)->s_clustersize_bits;
>>> +	clusters = ocfs2_clusters_for_bytes(sb, pos + count) - cpos;
>>> +
>>> +	while (clusters) {
>>> +		ret = ocfs2_get_clusters(inode, cpos, &phys_cpos, &extent_len,
>>> +					 &extent_flags);
>>> +		if (ret < 0) {
>>> +			mlog_errno(ret);
>>> +			goto out;
>>> +		}
>>> +
>>> +		if (phys_cpos == 0) {
>>> +			ret = 1;
>>> +			goto out;
>>> +		}
>>> +
>>> +		if (extent_len > clusters)
>>> +			extent_len = clusters;
>>> +
>>> +		clusters -= extent_len;
>>> +		cpos += extent_len;
>>> +	}
>>> +out:
>>> +	return ret;
>>> +}
>>> +
>>>    static ssize_t ocfs2_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>>>    {
>>>    	struct file *file = iocb->ki_filp;
>>>    	struct inode *inode = file->f_mapping->host;
>>>    	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>>>    	get_block_t *get_block;
>>> +	int ret;
>>>    
>>>    	/*
>>>    	 * Fallback to buffered I/O if we see an inode without
>>> @@ -2429,9 +2469,16 @@ static ssize_t ocfs2_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>>>    		return 0;
>>>    
>>>    	/* Fallback to buffered I/O if we do not support append dio. */
>>> -	if (iocb->ki_pos + iter->count > i_size_read(inode) &&
>>> -	    !ocfs2_supports_append_dio(osb))
>>> -		return 0;
>>> +	if (!ocfs2_supports_append_dio(osb)) {
>>> +		if (iocb->ki_pos + iter->count > i_size_read(inode))
>>> +			return 0;
>>> +
>>> +		ret = ocfs2_range_has_holes(inode, iocb->ki_pos, iter->count);
>>> +		if (ret == 1)
>>> +			return 0;
>>> +		else if (ret < 0)
>>> +			return ret;
>>> +	}
>>>    
>>>    	if (iov_iter_rw(iter) == READ)
>>>    		get_block = ocfs2_lock_get_block;
>>>
>>
>>
>