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Date:   Mon, 24 Dec 2018 11:00:12 +0900
From:   Tomasz Chmielewski <mangoo@wpkg.org>
To:     linux-btrfs@vger.kernel.org
Subject: Re: compress-force not really forcing compression?
Message-ID: <642827686bbbde2e359683c7e60743f9@wpkg.org>
Sender: linux-btrfs-owner@vger.kernel.org
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>> > If a file has portions which are not easily compressible does that imply all
>> > future writes are also incompressible. IMO no, so I think what will be prudent
>> > is remove FORCE_COMPRESS altogether and make the code act as if it's
>> > always on.
>> >
>> > Any opinions?
>> 
>> 
>> That is a good idea.  If I turn on compression I would expect 
>> everything
>> to be compressed, except in cases where there is no size benefit.
> 
> I expect that the vast majority of files consist of blocks of similar
> compressibility.  Thus, finding a block that fails to compress strongly
> suggests other blocks are either incompressible as well or compress 
> only
> minimally.  Refusing to waste time, electricity and fragmentation in 
> such
> case is a good default, I think.

Please see this thread for an example where btrfs compression fails to 
detect that text files compress very well:

https://marc.info/?t=144905015000003&r=1&w=4


To put it short - with rsync server receiving text logs from remote 
servers, sometimes at slow speeds (due to how logfiles are appended):

- compress + zlib - some 20% compression ratio
- compress-force + zlib - some 80% compression ratio


Tomasz Chmielewski
https://lxadm.com