Re: [PATCH 5/7] fsdax: Dedup file range to use a compare function

[Ruan Shiyang]

On 2021/2/10 下午9:19, Christoph Hellwig wrote:
> On Tue, Feb 09, 2021 at 05:46:13PM +0800, Ruan Shiyang wrote:
> > On 2021/2/9 下午5:34, Christoph Hellwig wrote:
> > > On Tue, Feb 09, 2021 at 05:15:13PM +0800, Ruan Shiyang wrote:
> > > > The dax dedupe comparison need the iomap_ops pointer as argument, so my
> > > > understanding is that we don't modify the argument list of
> > > > generic_remap_file_range_prep(), but move its code into
> > > > __generic_remap_file_range_prep() whose argument list can be modified to
> > > > accepts the iomap_ops pointer.  Then it looks like this:
> > >
> > > I'd say just add the iomap_ops pointer to
> > > generic_remap_file_range_prep and do away with the extra wrappers.  We
> > > only have three callers anyway.
> >
> > OK.
>
> So looking at this again I think your proposal actaully is better,
> given that the iomap variant is still DAX specific.  Sorry for
> the noise.
>
> Also I think dax_file_range_compare should use iomap_apply instead
> of open coding it.

There are two files, which are not reflinked, need to be direct_access() 
here.  The iomap_apply() can handle one file each time.  So, it seems 
that iomap_apply() is not suitable for this case...


The pseudo code of this process is as follows:

  srclen = ops->begin(&srcmap)
  destlen = ops->begin(&destmap)

  direct_access(&srcmap, &saddr)
  direct_access(&destmap, &daddr)

  same = memcpy(saddr, daddr, min(srclen,destlen))

  ops->end(&destmap)
  ops->end(&srcmap)

I think a nested call like this is necessary.  That's why I use the open 
code way.


--
Thanks,
Ruan Shiyang.
>