Improve performance of 10_linux_zfs

[Jean-Baptiste Lallement]

Performance of 10_linux_zfs decreases with the number of datasets, snapshot and clones.

2 parts can be improved:
  1. Cache repeating ZFS operations in the generation of the list of zfs entries and optimize the code path for the default layout on Ubuntu
  2. Grub menu operation executes lot of expensive "sed" operations just to add indentations which can be cached too.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: grub2 (not installed)
ProcVersionSignature: Ubuntu 5.4.0-18.22-generic 5.4.24
Uname: Linux 5.4.0-18-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu21
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Tue Mar 31 15:32:10 2020
InstallationDate: Installed on 2014-07-15 (2086 days ago)
InstallationMedia: Ubuntu 14.10 "Utopic Unicorn" - Alpha amd64 (20140520)
SourcePackage: grub2
UpgradeStatus: Upgraded to focal on 2018-03-24 (737 days ago)

[HARI NARAYAN MAHTO (hnm555)]

install ubuntu. then run boot-repair in terminal to fix this via liveusb then try to reboot system. i fixed this and now i'm able to boot into ubuntu 20.04.

[Launchpad Janitor (janitor)]

This bug was fixed in the package grub2 - 2.04-1ubuntu23

---------------
grub2 (2.04-1ubuntu23) focal; urgency=medium

  [ Jean-Baptiste Lallement ]
  [ Didier Roche ]
  * Performance improvements for update-grub on ZFS systems (LP: #1869885)

 -- Didier Roche <email address hidden> Tue, 31 Mar 2020 15:30:36 +0200