Re: [PATCH v3 1/2] ext4: Pass in DIO_SKIP_DIO_COUNT flag if inode_dio_begin() called

[Waiman Long]

On 04/25/2016 07:48 AM, Christoph Hellwig wrote:
> On Thu, Apr 21, 2016 at 02:15:24PM -0400, Waiman Long wrote:
> > On 04/20/2016 04:58 PM, Christoph Hellwig wrote:
> > > FYI, none of the Dax code even needs to ever touch the dio_count,
> > > as dax I/O can't be asynchronous, and we thus don't need it to protect
> > > against truncate.  I'd suggest to remove it and then end_io callback
> > >from the DAX code entirely as a start and then move from there.
> >
> > Yes, it seems like we may not need to change the dio_count in dax_do_io()
> > after all. BTW, what do mean by using end_io callback as a start?
> I mean to remove both the i_dio_count manipulation, and the unessecary
> end_io callback from dax_do_io.

Thanks for the clarification.

Since DAX I/O is always synchronous, the locking done by the caller or 
in the dax_do_Io() for read should be enough to prevent truncation from 
happening at the same time. So we don't need to use i_dio_count for that 
purpose.

However, I have not understood enough of the block IO layer to determine 
if the end_io callback is really redundant. I am not confident enough to 
touch the end_io callback.

Cheers,
Longman