On 2019/6/27 下午10:58, David Sterba wrote:
> On Tue, Jun 25, 2019 at 04:24:57PM +0800, Qu Wenruo wrote:
>> Ping?
>>
>> This patch should fix the problem of compressed extent even when
>> nodatasum is set.
>>
>> It has been one year but we still didn't get a conclusion on where
>> force_compress should behave.
> 
> Note that pings to patches sent year ago will get lost, I noticed only
> because you resent it and I remembered that we had some discussions,
> without conclusions.
> 
>> But at least to me, NODATASUM is a strong exclusion for compress, no
>> matter whatever option we use, we should NEVER compress data without
>> datasum/datacow.
> 
> That's correct, but the way you fix it is IMO not right. This was also
> noticed by Nikolay, that there are 2 locations that call
> inode_need_compress but with different semantics.
> 
> One is the decision if compression applies at all,

> and the second one
> when that's certain it's compression, to do it or not based on the
> status decision of eg. heuristics.

The second call is in compress_file_extent(), with inode_need_compress()
return 0 for NODATACOW/NODATASUM inodes, we will not go into
cow_file_range_async() branch at all.

So would you please explain how this could cause problem?
To me, prevent the problem in inode_need_compress() is the safest location.

Thanks,
Qu