Re: [PATCH -next v2 03/22] ext4: only order data when partially block truncating down

[Zhang Yi <yizhang089@gmail.com>]

On 2/10/2026 10:07 PM, Jan Kara wrote:
> On Tue 10-02-26 20:02:51, Zhang Yi wrote:
>> On 2/9/2026 4:28 PM, Zhang Yi wrote:
>>> On 2/6/2026 11:35 PM, Jan Kara wrote:
>>>> On Fri 06-02-26 19:09:53, Zhang Yi wrote:
>>>>> On 2/5/2026 11:05 PM, Jan Kara wrote:
>>>>>> So how about the following:
>>>>>
>>>>> Let me see, please correct me if my understanding is wrong, ana there are
>>>>> also some points I don't get.
>>>>>
>>>>>> We expand our io_end processing with the
>>>>>> ability to journal i_disksize updates after page writeback completes. Then
>>
>> While I was extending the end_io path of buffered_head to support updating
>> i_disksize, I found another problem that requires discussion.
>>
>> Supporting updates to i_disksize in end_io requires starting a handle, which
>> conflicts with the data=ordered mode because folios written back through the
>> journal process cannot initiate any handles; otherwise, this may lead to a
>> deadlock. This limitation does not affect the iomap path, as it does not use
>> the data=ordered mode at all.  However, in the buffered_head path, online
>> defragmentation (if this change works, it should be the last user) still uses
>> the data=ordered mode.
> 
> Right and my intention was to use reserved handle for the i_disksize update
> similarly as we currently use reserved handle for unwritten extent
> conversion after page writeback is done.
> 
> 								Honza

IIUC, reserved handle only works for ext4_jbd2_inode_add_wait(). It 
doesn't work for ext4_jbd2_inode_add_write() because writebacks 
triggered by the journaling process cannot initiate any handles, 
including reserved handles. So, I guess you're suggesting that within 
mext_move_extent(), we should proactively submit the blocks after 
swapping, and then call ext4_jbd2_inode_add_wait() to replace the 
existing ext4_jbd2_inode_add_write(). Is that correct?

Thanks,
Yi.