Hi,

This desktop@ thread [1] about a slow device restored by enabling fstrim.service, got me thinking about enabling fstrim.timer [2] by default in Fedora Workstation. But I'm curious if it might be desirable in other Fedora Editions, and making it a system-wide change?

I've checked recent versions of openSUSE and Ubuntu, and they have it enabled. Therefore I estimate the likelihood of running into cons (below) is pretty remote. Most people won't notice anything.

The pros: + when passed down to flash drives that support trim, it provides a hint to the drive firmware about erase blocks ready for erasure. Some devices will have improved wear leveling and performance as a result, but this is firmware specific. LVM [3] and dm-crypt [4] passdown appears to be enabled by default on Fedora. + with LVM thin provisioning, it will cause unused LV extents to be returned to the thin pool for use by other LVs, kind of a nifty work around for XFS not supporting fs shrink resize.

The gotchas: + Few, but highly visible, reports of buggy SSDs that corrupt or lose data soon after trim being issued. By now, most have been blacklisted in the kernel, and/or have manufacturer firmware updates. We shouldn't run into this problem unless someone has older hardware that hasn't been update and for some reason also hasn't been blacklisted in the kernel. + Older SSD's have only non-queued trim support, which also can result in a brief hang while the command is processed. This is highly variable based on the device firmware, and the workload. But using weekly fstrim is preferred for these devices, instead of using the discard mount option in /etc/fstab. + Possible exposure of fs locality pattern may be a security risk for some workflows. [4] [5]

[1] https://lists.fedoraproject.org/archives/list/desktop@lists.fedoraproject.or...

[2] fstrim.timer, if enabled, runs fstrim.service weekly, specifically Monday at midnight local time; and if the system isn't available at that time, it runs during or very soon after the next startup. The command: ExecStart=/usr/sbin/fstrim --fstab --verbose --quiet

fstab means only file systems in fstab are included; verbose reports the mount point and bytes potentially discarded and is recorded in the systemd journal; quiet suppresses errors which is typical for file systems and devices that don't support fstrim, e.g. the EFI System partition, which is FAT16/32; and USB flash "stick" drives, and hard drives.

[3] /etc/lvm/lvm.conf, if I'm reading it correctly, file system discards are passed down: # This configuration option has an automatic default value. # thin_pool_discards = "passdown"

Due to this Fedora 27 feature; trim is passed down by dm-crypt as well for LUKS volumes. Curiously because Fedora neither sets the discard mount option for any file system, nor enables fstrim.timer, this feature isn't being taken advantage of.

[4] https://fedoraproject.org/wiki/Changes/EnableTrimOnDmCrypt

[5] Trim on LUKS/dm-crypt note from upstream, section 5.19 https://gitlab.com/cryptsetup/cryptsetup/-/wikis/FrequentlyAskedQuestions#5-...