The `zfs_arc_max` setting *is* respected when I set it to a value of
`1073741824` = 1GiB
```
cat /etc/modprobe.d/zfs.conf; cat /sys/module/zfs/parameters/zfs_arc_max; cat
/proc/spl/kstat/zfs/arcstats |grep ^size -B3
options zfs zfs_arc_max=1073741824
1073741824
c 41073741824
c_min 4519804800
c_max 41073741824
size41086124448
```
The manpage `man zfs-module-parameters` says
```
zfs_arc_max (ulong)
Max arc size of ARC in bytes. If set to 0 then it will consume 1/2 of system
RAM. This value must be at least 67108864 (64 megabytes).
This value can be changed dynamically with some caveats. It cannot be
set back to 0 while running and reducing it below the current ARC size
will not cause the ARC to shrink without memory pressure to induce
shrinking.
Default value: 0.
```
Before I had set it to `134217728`, more than 64MiB, but it was not
respected.
I also tried setting `zfs_arc_max` to `519804800` (495.7MiB, where ever
this number comes from), the value reported as `c_min` and it *not*
respected.
So, the minimum arc size seems to be around 1GB and *not* 64MB, as the
manpage claims. (documentation lies, the code does not)
--
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to zfs-linux in Ubuntu.
https://bugs.launchpad.net/bugs/1854480
Title:
zfs_arc_max not working anymore in zfs 0.8.1
Status in zfs-linux package in Ubuntu:
Fix Released
Bug description:
In the past I could limit the size of L1ARC by specifying "options zfs
zfs_arc_max=3221225472" in /etc/modprobe.d/zfs.conf. I tried even to
fill /sys/module/zfs/parameters/zfs_arc_max directly, but none of
those methods limits the size of L1ARC. It worked nicely in zfs 0.7.x.
Nowadays I use a nvme drive with 3400 MB/s read throughput and I see
not much difference between e.g booting the system from nvme and
rebooting the system from L1ARC. Having a 96-99% hit rate for the
L1ARC, I like to free up some memory, thus avoiding some delay of
freeing memory from L1ARC while loading a VM.
-
UPDATE:
The system only limits the L1ARC, if we directly after the login write
the zfs_arc_max value to the file
/sys/module/zfs/parameters/zfs_arc_max.
ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: zfsutils-linux 0.8.1-1ubuntu14.1
ProcVersionSignature: Ubuntu 5.3.0-23.25-generic 5.3.7
Uname: Linux 5.3.0-23-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu8.2
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Fri Nov 29 06:19:15 2019
InstallationDate: Installed on 2019-11-25 (3 days ago)
InstallationMedia: Ubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
SourcePackage: zfs-linux
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.sudoers.d.zfs: [inaccessible: [Errno 13] Permission
denied: '/etc/sudoers.d/zfs']
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