Re: [PATCH 1/2] btrfs: inode: Don't compress if NODATASUM or NODATACOW set

[Anand Jain <anand.jain@oracle.com>]

On 27/6/19 10:58 PM, 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 I wonder what's the reason that datasum/datacow is prerequisite 
for the compression ?

Thanks, Anand

>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.
>