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

[Zhang Yi]

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.