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List:       fedora-devel-list
Subject:    Re: Btrfs by default, the compression option
From:       Dominique Martinet <asmadeus () codewreck ! org>
Date:       2020-07-08 9:21:29
Message-ID: 20200708092129.GA10608 () nautica
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Kamil Paral wrote on Wed, Jul 08, 2020:
> On Wed, Jul 8, 2020 at 8:26 AM Chris Murphy <lists@colorremedies.com> wrote:
> 
> > D. Which directories? Some may be outside of the installer's scope.
> >
> > /usr
> > /var/lib/flatpak
> > ~/.local/share/flatpak
> 
> I have a concern regarding games. Currently, we have a few a bit more
> demanding titles on Flathub already, like 0AD, Xonotic or Albion Online. In
> the glorious future (tm) we might get more. Games are very sensitive to
> available CPU cycles and context switching and usually come with their data
> files already compressed. Including the btrfs compression by default on
> flatpak dirs could lead to lowered performance whenever the game tries to
> load some assets (older titles do that during the loading screen, newer
> titles stream new assets constantly during gameplay and any slowdown
> manifests as game stuttering).

Please test, but if a file is deemed not compressible (based on, not
sure what? the first few blocks?) then it will be stored in the
non-compressed version.
You can check with compsize after the fact if the file had been
compressed or not.

This should be true unless the compress-force mount option is used, even
the chattr is only a hint


> I'm personally more concerned about reduced performance in e.g. my web
> browser than disk wear out. I don't see much harm in compressing /usr,
> because it's a read-only location that gets loaded once when the app starts
> (it might delay the app startup a bit, though, and decrease the perceived
> snappiness of the desktop). But I'm concerned about compressing locations
> which are hit often, like ~/.var or ~/.cache. I've had my 120GB SSD for 5
> years and I'm just at 10% of expected TBW (total bytes written). If the SSD
> lasts 50 or 100 years is not really important for me, but the desktop and
> app responsiveness is (and game performance, of course:)). I think write
> amplification is a problem specific to devices with SD cards, and for
> anyone else, it might be better to leave it unset and let people enable it
> (it's simple) if they want it for their use case.

This obviously needs testing on a wide variety of hardware but I haven't
noticed any difference in the feeling on an intel laptop (kabylake i5
throttled at 2GHz) ; that being said firefox isn't the most responsive
app in my book...

-- 
Dominique
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