Ocfs2 devel - Dec 2017 - [PATCH] ocfs2: fall back to buffer IO when append dio is disabled with file hole existing

On 17/12/19 05:53, Andrew Morton wrote:
> On Mon, 18 Dec 2017 12:06:21 +0000 Changwei Ge <ge.changwei at
h3c.com> wrote:
> 
>> Before ocfs2 supporting allocating clusters while doing append-dio, all
append
>> dio will fall back to buffer io to allocate clusters firstly. Also,
when it
>> steps on a file hole, it will fall back to buffer io, too. But for
current
>> code, writing to file hole will leverage dio to allocate clusters. This
is not
>> right, since whether append-io is enabled tells the capability whether
ocfs2 can
>> allocate space while doing dio.
>> So introduce file hole check function back into ocfs2.
>> Once ocfs2 is doing dio upon a file hole with append-dio disabled, it
will fall
>> back to buffer IO to allocate clusters.
>>
> 
> hm, that's a bit hard to understand.  Hopefully reviewers will know
> what's going on ;)> 
Also suggest rearrange the description:)
>> --- a/fs/ocfs2/aops.c
>> +++ b/fs/ocfs2/aops.c
>> @@ -2414,6 +2414,44 @@ 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).
>> + */
>> +static int ocfs2_check_range_for_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 || (extent_flags & OCFS2_EXT_UNWRITTEN)) {
>> +			ret = 1;
>> +			break;
>> +		}
>> +
>> +		if (extent_len > clusters)
>> +			extent_len = clusters;
>> +
>> +		clusters -= extent_len;
>> +		cpos += extent_len;
>> +	}
>> +out:
>> +	return ret;
>> +}
> 
> A few thoughts:
> 
> - a function which does "check_foo" isn't well named. 
Because the
>   reader cannot determine whether the return value means "foo is
true"
>   or "foo is false".
> 
>   So a better name for this function is ocfs2_range_has_holes(), so
>   the reader immediately understand what its return value *means".
> 
>   Also a bool return value is more logical.
> 
> - Mixing "goto out" with "break" as above is a bit odd.
> 
> So...
> 
> 
> ---
a/fs/ocfs2/aops.c~ocfs2-fall-back-to-buffer-io-when-append-dio-is-disabled-with-file-hole-existing-fix
> +++ a/fs/ocfs2/aops.c
> @@ -2469,10 +2469,9 @@ static int ocfs2_dio_end_io(struct kiocb
>   * Will look for holes and unwritten extents in the range starting at
>   * pos for count bytes (inclusive).
>   */
> -static int ocfs2_check_range_for_holes(struct inode *inode, loff_t pos,
> -				       size_t count)
> +static bool ocfs2_range_has_holes(struct inode *inode, loff_t pos, size_t
count)
>  {
> -	int ret = 0;
> +	bool ret = false;
I have a different opinion here. If we change return value from int to
bool, the error returned by ocfs2_get_clusters cannot be reflected. So
I'd prefer the original version.

Thanks,
Joseph
>  	unsigned int extent_flags;
>  	u32 cpos, clusters, extent_len, phys_cpos;
>  	struct super_block *sb = inode->i_sb;
> @@ -2489,8 +2488,8 @@ static int ocfs2_check_range_for_holes(s
>  		}
>  
>  		if (phys_cpos == 0 || (extent_flags & OCFS2_EXT_UNWRITTEN)) {
> -			ret = 1;
> -			break;
> +			ret = true;
> +			goto out;
>  		}
>  
>  		if (extent_len > clusters)
> _
>

On Tue, 19 Dec 2017 09:24:17 +0800 Joseph Qi <jiangqi903 at gmail.com>
wrote:
> > ---
a/fs/ocfs2/aops.c~ocfs2-fall-back-to-buffer-io-when-append-dio-is-disabled-with-file-hole-existing-fix
> > +++ a/fs/ocfs2/aops.c
> > @@ -2469,10 +2469,9 @@ static int ocfs2_dio_end_io(struct kiocb
> >   * Will look for holes and unwritten extents in the range starting at
> >   * pos for count bytes (inclusive).
> >   */
> > -static int ocfs2_check_range_for_holes(struct inode *inode, loff_t
pos,
> > -				       size_t count)
> > +static bool ocfs2_range_has_holes(struct inode *inode, loff_t pos,
size_t count)
> >  {
> > -	int ret = 0;
> > +	bool ret = false;
> 
> I have a different opinion here. If we change return value from int to
> bool, the error returned by ocfs2_get_clusters cannot be reflected. So
> I'd prefer the original version.
But that error code is not used?

On 2017/12/19 9:24, Joseph Qi wrote:
> 
> On 17/12/19 05:53, Andrew Morton wrote:
>> On Mon, 18 Dec 2017 12:06:21 +0000 Changwei Ge <ge.changwei at
h3c.com> wrote:
>>
>>> Before ocfs2 supporting allocating clusters while doing append-dio,
all append
>>> dio will fall back to buffer io to allocate clusters firstly. Also,
when it
>>> steps on a file hole, it will fall back to buffer io, too. But for
current
>>> code, writing to file hole will leverage dio to allocate clusters.
This is not
>>> right, since whether append-io is enabled tells the capability
whether ocfs2 can
>>> allocate space while doing dio.
>>> So introduce file hole check function back into ocfs2.
>>> Once ocfs2 is doing dio upon a file hole with append-dio disabled,
it will fall
>>> back to buffer IO to allocate clusters.
>>>
>>
>> hm, that's a bit hard to understand.  Hopefully reviewers will know
>> what's going on ;)>
> Also suggest rearrange the description:)
Hi Joseph,
OK, I will elaborate the intention of this patch further in the next version.
> 
>>> --- a/fs/ocfs2/aops.c
>>> +++ b/fs/ocfs2/aops.c
>>> @@ -2414,6 +2414,44 @@ 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).
>>> + */
>>> +static int ocfs2_check_range_for_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 || (extent_flags & OCFS2_EXT_UNWRITTEN))
{
>>> +			ret = 1;
>>> +			break;
>>> +		}
>>> +
>>> +		if (extent_len > clusters)
>>> +			extent_len = clusters;
>>> +
>>> +		clusters -= extent_len;
>>> +		cpos += extent_len;
>>> +	}
>>> +out:
>>> +	return ret;
>>> +}
>>
>> A few thoughts:
>>
>> - a function which does "check_foo" isn't well named. 
Because the
>>    reader cannot determine whether the return value means "foo is
true"
>>    or "foo is false".
>>
>>    So a better name for this function is ocfs2_range_has_holes(), so
>>    the reader immediately understand what its return value
*means".
>>
>>    Also a bool return value is more logical.
>>
>> - Mixing "goto out" with "break" as above is a bit
odd.
>>
>> So...
>>
>>
>> ---
a/fs/ocfs2/aops.c~ocfs2-fall-back-to-buffer-io-when-append-dio-is-disabled-with-file-hole-existing-fix
>> +++ a/fs/ocfs2/aops.c
>> @@ -2469,10 +2469,9 @@ static int ocfs2_dio_end_io(struct kiocb
>>    * Will look for holes and unwritten extents in the range starting at
>>    * pos for count bytes (inclusive).
>>    */
>> -static int ocfs2_check_range_for_holes(struct inode *inode, loff_t
pos,
>> -				       size_t count)
>> +static bool ocfs2_range_has_holes(struct inode *inode, loff_t pos,
size_t count)
>>   {
>> -	int ret = 0;
>> +	bool ret = false;
> 
> I have a different opinion here. If we change return value from int to
> bool, the error returned by ocfs2_get_clusters cannot be reflected. So
> I'd prefer the original version.
Yes, it's my mistake here.
You have to forgive me.:)

Thanks,
Changwei
> 
> Thanks,
> Joseph
> 
>>   	unsigned int extent_flags;
>>   	u32 cpos, clusters, extent_len, phys_cpos;
>>   	struct super_block *sb = inode->i_sb;
>> @@ -2489,8 +2488,8 @@ static int ocfs2_check_range_for_holes(s
>>   		}
>>   
>>   		if (phys_cpos == 0 || (extent_flags & OCFS2_EXT_UNWRITTEN)) {
>> -			ret = 1;
>> -			break;
>> +			ret = true;
>> +			goto out;
>>   		}
>>   
>>   		if (extent_len > clusters)
>> _
>>
>