On Sun, Jan 5, 2020 at 5:24 AM Bohdan Khomutskyi <bkhom...@redhat.com> wrote: > > Summary > > Improve compression ratio of SquashFS filesystem on the installation media.
On the issues of Fedora ISOs using excessive CPU, related to lzma decompression: https://bugzilla.redhat.com/show_bug.cgi?id=1717728 https://pagure.io/releng/issue/8581 Create images using plain squashfs (without nested ext4) https://pagure.io/releng/issue/8646 And koji issue to enhance it so it can accept configurable rootfs types (plain squashfs and configurable compression) https://pagure.io/koji/issue/1622 I'm wondering if you can relate this feature proposal to those issues and feature requests? In my testing, xz does provide better compression ratios, well suited for seldom used images like archives. But it really makes the installation experience worse by soaking the CPU, times thousands of installations (openQA tests on every single nightly, every human QA tester for nightlies, betas, and then the final released product used by Fedora end users). Has zstandard been evaluated? In my testing of images compressed with zstd, the CPU hit is cut by more than 50%, and is no longer a bottleneck during installations. Image size does increase, although I haven't tested mksquashfs block size higher than 256K. Using zstd with Fedora images also builds on prior evaluation, testing, and effort moving RPM from xz to zstd. My testing with mksquashfs block size suggests compression ratio improves but latency gets worse, and becomes somewhat pathological with a nested ext4 in it: my best guess is the random access nature of ext4, many 4KiB seeks turn into larger 128KiB seeks; and also squashfs and ext4 probably have different localities (where data is placed in relation to their metadata, in attempt to optimize). Dropping the nested ext4 image also improved performance quite a bit, independent of compression algorithm. I forget how much exactly but it may be ~30%. I've pretty much concluded Fedora is best off dropping the nested ext4 in favor of plain squashfs, and using zstd. It's not required to do both, but the benefit is additive and significant. The work in dracut and lorax to support plain squashfs, assembling it using overlayfs instead of device-mapper is already done, and tested. -- Chris Murphy _______________________________________________ devel mailing list -- devel@lists.fedoraproject.org To unsubscribe send an email to devel-le...@lists.fedoraproject.org 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@lists.fedoraproject.org
