Can't to create more than one /dev/zram0 devices

[igreenman]

Can't to create more than one /dev/zram0 devices.

no zram devices with uncommented zram[streams]=${sys[cpu_count]} in /etc/systemd-swap.conf

See bug FS#41361 in archlinux bugzilla.

[nefelim4ag]

This not a bug, check:
cat /sys/block/zram0/max_comp_streams
Official kernel documentation:
https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next/+/refs/heads/akpm/Documentation/blockdev/zram.txt
quote:
2) Set max number of compression streams
Compression backend may use up to max_comp_streams compression streams,
thus allowing up to max_comp_streams concurrent compression operations.
By default, compression backend uses single compression stream.
Examples:
#show max compression streams number
cat /sys/block/zram0/max_comp_streams
#set max compression streams number to 3
echo 3 > /sys/block/zram0/max_comp_streams

[igreenman]

Agree I'm a little confused.
The previous version was the option zram_num_devices=$cpu_count.
And even when the option was commented out was two zram devices.
The latest version is only one zram device. Is that correct?
The system has two CPUs.

[nefelim4ag]

Yes, previously i use several zram devices like https://aur.archlinux.org/packages/zramswap
After i found max_comp_streams options and rewrite some code for using kernel side feature.
And now, setup several zram devices for swap no needed, i can only set compression streams count with one zram device.

And even when the option was commented out was two zram devices. - if options commented and script setup several devices -> this is a bug of previously version.

The latest version is only one zram device. Is that correct?
The system has two CPUs.
Latest version setup only one device and if options for multi compression streams enabled, set 2 threads in max_comp_streams for your system.
This is right behavior.

[igreenman]

About zram[streams] option.

1. How to set max_comp_streams correctly systemwide?
2. Not very logical that if in config zram[streams] more than max_comp_streams, then the zram device is not created.

[nefelim4ag]

1. Systemwide? Only with hands :)
   echo | sudo tee /sys/block/zram*/max_comp_streams
2. I repeat again, zram[streams] == max_comp_streams
   in script echo ${zram[streams]} > /sys/block/zram${[dev]}/max_comp_streams
   Value from zram[streams] sets to max_comp_streams
   if you set zram[streams]=4, after starting systemd-swap in max_comp_streams you have 4.
   We no need to create several device, 1 enough.
   Or in your system after set zram[streams]=4 zram device not setup? May be you not install zramctl? (this is external depends for systemd-swap, and this heeded for setups zram devices in script)

[igreenman]

FS#41361:
no zram devices with uncommented zram[streams]=${sys[cpu_count]} in /etc/systemd-swap.conf

And one /dev/zram0 with this string commented.

Second line means that zramctl is installed, isn't it?

[nefelim4ag]

I am confused, in arch bug tracker you create bug because my tool no setup zram devices if you set streams count in config, on github you say what my tool must setup several device.

I retest on my system and all working perfect. If you have trouble please provide additional info, like steps for reproduce. Config copy paste, logs, some thing, what I can using for fix that.
one line command:
sudo bash -cx 'uname -a; modprobe --first-time zram; cd /etc/modprobe.d/; grep . *; ls /sys/block/; mount; swapon; zramctl status; cat /etc/systemd-swap.conf; bash -x /usr/lib/systemd/scripts/systemd-swap.sh stop; bash -x /usr/lib/systemd/scripts/systemd-swap.sh start; mount; swapon; zramctl status; ls /sys/block/; ls /sys/block/zram0/; strace zramctl find 1024M lz4 4;' &> ~/systemd-swap.log

[nefelim4ag]

if you using kernel => 3.15 and not set zram[alg] option, and set zram[streams] - you can get case where zramctl can't work properly, i fix that in 2.24.5

[igreenman]

I apologize for the delay. I do not have access to the system right now.
Yes, the system has been in up to date conditions of a week ago (kernel ~3.15.5)
And I did not set zram[alg] option.
Thank you.

[nefelim4ag]

Happy to help, so can you close issue and bug report? https://bugs.archlinux.org/task/41361