Re: [PATCH 1/1] ext4: Remove empty index blocks when punching holes

[Allison Henderson <achender@linux.vnet.ibm.com>]

On 02/29/2012 12:44 AM, Lukas Czerner wrote:
> On Wed, 29 Feb 2012, Allison Henderson wrote:
>
>> When punching holes, it is possible that all the entries of an
>> index block may be removed.  These empty index blocks need to
>> be removed once punch hole completes.  This patch adds some extra
>> logic to the punch hole code to remove empty index blocks.
>
> Hi Allison,
>
> I have not looked at the patch, but just to let you know. I am working
> on a patch to reorganize the punch hole support a bit in order to fix
> a bug I found but more importantly to make it faster, better
> understandable and to reuse more of an existing code paths.
>
> I am cleaning up the patches and testing them right now, so hopefully by
> the end of the week I'll send those out.
>
> Thanks!
> -Lukas
>

Hi Lukas,

Alrighty then, sounds good.  This patch seemed to correct the loop 
discard bug we saw earlier for me.  So please make sure you have some 
similar fix in your new patch.  Basically we had some extra index blocks 
hanging around when the depth was greater than one, so the patch just 
adds some code to free up those index blocks in the path if they are 
empty.  Hope this helps!  Thx!  :)

Allison Henderson

>>
>> Signed-off-by: Allison Henderson<achender@linux.vnet.ibm.com>
>> ---
>> :100644 100644 ad39627... 6bb2f55... M	fs/ext4/extents.c
>>   fs/ext4/extents.c |   17 ++++++++++++++++-
>>   1 files changed, 16 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>> index ad39627..6bb2f55 100644
>> --- a/fs/ext4/extents.c
>> +++ b/fs/ext4/extents.c
>> @@ -3709,7 +3709,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
>>   	struct ext4_extent newex, *ex, *ex2;
>>   	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
>>   	ext4_fsblk_t newblock = 0;
>> -	int free_on_err = 0, err = 0, depth, ret;
>> +	int free_on_err = 0, err = 0, depth, ret, i;
>>   	unsigned int allocated = 0, offset = 0;
>>   	unsigned int allocated_clusters = 0, reserved_clusters = 0;
>>   	unsigned int punched_out = 0;
>> @@ -3880,6 +3880,21 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
>>   			err = ext4_ext_rm_leaf(handle, inode, path,
>>   					&partial_cluster, map->m_lblk,
>>   					       map->m_lblk + punched_out);
>> +			if (err)
>> +				goto out2;
>> +
>> +			/*
>> +			 * Walk back up the path and remove
>> +			 * empty index blocks
>> +			 */
>> +			for (i = depth - 1; i>  0; i--) {
>> +				if (path[i].p_hdr->eh_entries == 0) {
>> +					err = ext4_ext_rm_idx(handle, inode,
>> +								path + i);
>> +					if (err)
>> +						goto out2;
>> +				}
>> +			}
>>
>>   			if (!err&&  path->p_hdr->eh_entries == 0) {
>>   				/*
>>
>