Public bug reported:
[Impact]
ZFS ignores tunable "zfs_arc_max" due to it being below allmem/32 threshold.
This prevents users from properly restraining ARC sizes, and can cause
increased memory contention in some systems.
[Test Plan]
1. Deploy test system with ZFS storage and 32GB RAM
2. Add ARC tunables to /etc/modprobe.d/99-zfs-arc.conf
# cat /etc/modprobe.d/99-zfs-arc.conf
options zfs zfs_arc_min=536870912
options zfs zfs_arc_max=966367641
3. Reboot system
4. Verify ARC sizes through "arc_summary"
# arc_summary | grep -A3 "ARC size"
ARC size (current): < 0.1 % 1.3 MiB
Target size (adaptive): 100.0 % 15.7 GiB
Min size (hard limit): 3.2 % 512.0 MiB
Max size (high water): 31:1 15.7 GiB
For a 32GB test system, we should be able to set max ARC sizes below
1GB.
[Fix]
This has been fixed by upstream commit:
- 36a6e2335c45 "Don't ignore zfs_arc_max below allmem/32"
The commit has been introduced in upstream zfs-2.0.0, so it's needed for
Bionic and Focal. Releases starting with Impish already have this commit
by default:
$ git describe --contains 36a6e2335c45
zfs-2.0.0-rc1~332
$ rmadison zfs-linux
zfs-linux | 0.7.5-1ubuntu15 | bionic | source
zfs-linux | 0.7.5-1ubuntu16.12 | bionic-updates | source
zfs-linux | 0.8.3-1ubuntu12 | focal | source
zfs-linux | 0.8.3-1ubuntu12.9 | focal-security | source
zfs-linux | 0.8.3-1ubuntu12.13 | focal-updates | source
zfs-linux | 0.8.3-1ubuntu12.14 | focal-proposed | source
zfs-linux | 2.0.6-1ubuntu2 | impish | source
zfs-linux | 2.0.6-1ubuntu2.1 | impish-updates | source
zfs-linux | 2.1.2-1ubuntu3 | jammy | source
[Regression Potential]
The introduced commit essentially removes the limitation of setting ARC
tunables below allmem/32, and re-arranges the order of how some of the tunables
are parsed. Regressions would possibly show up as other tunables being ignored
or not being set correctly due to parsing errors. We should validate whether
other ARC related tunables are still being set correctly, and whether ZFS is
using the set values for the ARC memory thresholds.
** Affects: zfs-linux (Ubuntu)
Importance: Undecided
Status: Fix Released
** Affects: zfs-linux (Ubuntu Bionic)
Importance: Medium
Assignee: Heitor Alves de Siqueira (halves)
Status: Confirmed
** Affects: zfs-linux (Ubuntu Focal)
Importance: Medium
Assignee: Heitor Alves de Siqueira (halves)
Status: Confirmed
** Tags: sts
** Changed in: zfs-linux (Ubuntu)
Status: New => Fix Released
** Also affects: zfs-linux (Ubuntu Bionic)
Importance: Undecided
Status: New
** Also affects: zfs-linux (Ubuntu Focal)
Importance: Undecided
Status: New
** Changed in: zfs-linux (Ubuntu Bionic)
Status: New => Confirmed
** Changed in: zfs-linux (Ubuntu Focal)
Status: New => Confirmed
** Changed in: zfs-linux (Ubuntu Bionic)
Importance: Undecided => Medium
** Changed in: zfs-linux (Ubuntu Focal)
Importance: Undecided => Medium
** Changed in: zfs-linux (Ubuntu Bionic)
Assignee: (unassigned) => Heitor Alves de Siqueira (halves)
** Changed in: zfs-linux (Ubuntu Focal)
Assignee: (unassigned) => Heitor Alves de Siqueira (halves)
** Description changed:
[Impact]
- ZFS ignores tunable "zfs_arc_max" due to it being below allmem/32
- threshold. This prevents users from properly restraining ARC sizes, and can
- cause increased memory contention in some systems.
+ ZFS ignores tunable "zfs_arc_max" due to it being below allmem/32 threshold.
This prevents users from properly restraining ARC sizes, and can cause
increased memory contention in some systems.
[Test Plan]
1. Deploy test system with ZFS storage and 32GB RAM
2. Add ARC tunables to /etc/modprobe.d/99-zfs-arc.conf
- # cat /etc/modprobe.d/99-zfs-arc.conf
- options zfs zfs_arc_min=536870912
- options zfs zfs_arc_max=966367641
+ # cat /etc/modprobe.d/99-zfs-arc.conf
+ options zfs zfs_arc_min=536870912
+ options zfs zfs_arc_max=966367641
3. Reboot system
4. Verify ARC sizes through "arc_summary"
- # arc_summary | grep -A3 "ARC size"
- ARC size (current): < 0.1 % 1.3 MiB
- Target size (adaptive): 100.0 % 15.7 GiB
- Min size (hard limit): 3.2 % 512.0 MiB
- Max size (high water): 31:1 15.7 GiB
+ # arc_summary | grep -A3 "ARC size"
+ ARC size (current): < 0.1 % 1.3 MiB
+ Target size (adaptive): 100.0 % 15.7 GiB
+ Min size (hard limit): 3.2 % 512.0 MiB
+ Max size (high water): 31:1 15.7 GiB
For a 32GB test system, we should be able to set max ARC sizes below
1GB.
[Fix]
This has been fixed by upstream commit:
- - 36a6e2335c45 "Don't ignore zfs_arc_max below allmem/32"
+ - 36a6e2335c45 "Don't ignore zfs_arc_max below allmem/32"
- The commit has been introduced in upstream zfs-2.0.0, so it's needed for
Bionic
- and Focal. Releases starting with Impish already have this commit by default:
+ The commit has been introduced in upstream zfs-2.0.0, so it's needed for
+ Bionic and Focal. Releases starting with Impish already have this commit
+ by default:
$ git describe --contains 36a6e2335c45
zfs-2.0.0-rc1~332
$ rmadison zfs-linux
- zfs-linux | 0.7.5-1ubuntu15 | bionic | source
- zfs-linux | 0.7.5-1ubuntu16.12 | bionic-updates | source
- zfs-linux | 0.8.3-1ubuntu12 | focal | source
- zfs-linux | 0.8.3-1ubuntu12.9 | focal-security | source
- zfs-linux | 0.8.3-1ubuntu12.13 | focal-updates | source
- zfs-linux | 0.8.3-1ubuntu12.14 | focal-proposed | source
- zfs-linux | 2.0.6-1ubuntu2 | impish | source
- zfs-linux | 2.0.6-1ubuntu2.1 | impish-updates | source
- zfs-linux | 2.1.2-1ubuntu3 | jammy | source
+ zfs-linux | 0.7.5-1ubuntu15 | bionic | source
+ zfs-linux | 0.7.5-1ubuntu16.12 | bionic-updates | source
+ zfs-linux | 0.8.3-1ubuntu12 | focal | source
+ zfs-linux | 0.8.3-1ubuntu12.9 | focal-security | source
+ zfs-linux | 0.8.3-1ubuntu12.13 | focal-updates | source
+ zfs-linux | 0.8.3-1ubuntu12.14 | focal-proposed | source
+ zfs-linux | 2.0.6-1ubuntu2 | impish | source
+ zfs-linux | 2.0.6-1ubuntu2.1 | impish-updates | source
+ zfs-linux | 2.1.2-1ubuntu3 | jammy | source
[Regression Potential]
- The introduced commit essentially removes the limitation of setting ARC
tunables
- below allmem/32, and re-arranges the order of how some of the tunables are
- parsed. Regressions would possibly show up as other tunables being ignored or
- not being set correctly due to parsing errors. We should validate whether
other
- ARC related tunables are still being set correctly, and whether ZFS is using
the
- set values for the ARC memory thresholds.
+ The introduced commit essentially removes the limitation of setting ARC
tunables below allmem/32, and re-arranges the order of how some of the tunables
are parsed. Regressions would possibly show up as other tunables being ignored
or not being set correctly due to parsing errors. We should validate whether
other ARC related tunables are still being set correctly, and whether ZFS is
using the set values for the ARC memory thresholds.
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https://bugs.launchpad.net/bugs/1964992
Title:
ZFS ignores ARC sizes below allmem/32
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