Hi, The change proposal has a 'compression option' and we kinda need to get organized. https://fedoraproject.org/wiki/Changes/BtrfsByDefault#Compression - Compression saves space, significantly reduces write amplification and therefore increases flash lifespan, and in some cases increases performance. - Desired but not a requirement of the change proposal. 1. Goal: probably the goal performance wise is to perform as good or better than now. Is it OK if there's a write time performance hit for a small percent of folks, for a high value target like usr that isn't updated that often, and is also updated out of band (offline updates typically, but also isn't something directly related to the daily workload)? How to decide this? 2. Benchmarking: this is hard. A simple tool for doing comparisons among algorithms on a specific bit of hardware is lzbench. https://github.com/inikep/lzbench How to compile on F32. https://github.com/inikep/lzbench/issues/69 But is that adequate? How do we confirm/deny on a wide variety of hardware that this meets the goal? And how is this test going to account for parallelization, and read ahead? Do we need a lot of data or is it adequate to get a sample "around the edges" (e.g. slow cpu fast drive; fast cpu slow drive; fast cpu fast drive; slow cpu slow drive). What algorithm? 3. Improvements and upgrades. We'll do plan A, but learn new things later, and come up with plan B. How do we get the plan A folks upgraded to plan B? Or just don't worry? 4. The whole file system (using a mount option) or curated (using an XATTR set on specific "high value" directories)? This part is elaborated below. A. do this with a mount option '-o compress=zstd:1' - dilemma: it doesn't always lead to equal or better performance. On some systems and workloads, write performance is slightly reduced. What about LZO? B. do this with per directory XATTR - dilemma: the target directories don't exist at install time, depending on whether the installation is rsync, rpm, or unsquashfs based. C. do the install with '-o compres=zstd', then set XATTR post-install - dilemma: the installed files won't have XATTR set, only new files inherit; does a 'dnf update' overwrite files and therefore the XATTR is not inherited, or are they new files and do inherit the XATTR? D. Which directories? Some may be outside of the installer's scope. /usr /var/lib/flatpak ~/.local/share/flatpak /var/lib/containers/ ~/.local/share/containers/ ~/.var ~/.cache (Plausible this list should be reversed. While compressing ~/.cache may not save much space, it's likely hammered with more changes than other locations, hence more benefit in terms of reducing write amplification.) For reference, the above is mostly from the description in the RFE bug attached to the feature's tracker bug. But I think it's best to have most discussion here and leave the bug for implementing+testing the implementation details. https://bugzilla.redhat.com/show_bug.cgi?id=1851276 Thanks, -- Chris Murphy _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx
