Do not activate not currently used LVM volumes #6184
Labels
C: core
C: storage
P: default
Priority: default. Default priority for new issues, to be replaced given sufficient information.
T: enhancement
Type: enhancement. A new feature that does not yet exist or improvement of existing functionality.
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marmarek
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T: enhancement
marmarek
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Jan 15, 2021
This prevents udev from accessing not currently used volumes, and also makes LVM snapshot operations faster (less locking to do). There is at least one unsolved problem here: inactive volumes do not have size listed on `lvs` output. There is a band-aid by caching the usage from the last time the volume was active, but it isn't enough for many cases (at the very least - reporting disk usage of a VM that wasn't started recently). There may be also other places that assume existing volumes always have relevant /dev/ node present. Fixes QubesOS/qubes-issues#6184
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The exact performance gain needs to be measured. I initially considered it for R4.1, but now I think it may be too risky change at this stage - if the benefits are not great, I'd rather postpone it for a later version. |
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The problem you're addressing (if any)
Active LVM volumes takes some kernel resources, but also activating them takes time. Active volumes also require more locking on LVM side when handling them - for example when creating a snapshot (volume clone) if source volume is active, it needs to be suspended. This takes time.
Describe the solution you'd like
Keep active only volumes currently in use by a running VM. Others should be inactive. LVM thin snapshots are inactive by default, unless explicitly requested to be activated (we the current LVM storage pool driver does). This require following change:
-knand-ayoptions fromlvcreatecalllvchange -aycall in the VM start pathlvchange -ancall in the VM shutdown pathWhere is the value to a user, and who might that user be?
Less resources used in dom0. Faster VM startup/shutdown time.
Relevant documentation you've consulted
https://dev.qubes-os.org/projects/core-admin/en/latest/qubes-storage.html
Related, non-duplicate issues
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