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

Ruan Shiyang
2021-02-17T03:24:27Z

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.