Subject: Re: zram not zramfs for swap

Maurice Kinal wrote to andy5995 on 08/31/2026 02:35 <=-

Hej andy5995!

Using zramfs is new to me, I've been using it for about a month. I
have 14GB Ram.

New to me as well. Offhand it sounds like /dev/ramX which I used to
use before I became familiar with the kernel's tmpfs. Comparing tmpfs with nvme0n1p2 - which I currently have mounted on /dev/lfs;

Hello Maurice!

I unintentionally gave you incorrect info. zram not zram fs.

[andy@prometheus build-asan](master)$ zramctl
NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 zstd 8G 1.2G 373M 388.1M [SWAP]

zram is a Linux kernel module that allows you to set up compressed >filesystems in RAM.

zram-tools uses this module to set up compressed swap space. This is useful >on systems with low memory or servers running a large amount of services with >data that's easily swappable but that you may wish to swap back fast without >sacrificing disk bandwidth.

By default it allocates a maximum of 50% of memory, although it only uses >what it needs. You can configure this in /etc/default/zramswap.

--
-Andy Alt

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Hey andy5995!

I unintentionally gave you incorrect info. zram not zram fs.

Happens all the time. I am meaning to research it but have been a tad distracted with the latest build. I'll try and catch up soon.

Life is good,
Maurice

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Hej andy5995!

# modinfo zram
filename: /lib/modules/7.2.3/kernel/drivers/block/zram/zram.ko.gz description: Compressed RAM Block Device
author: Nitin Gupta <ngupta@vflare.org>
license: Dual BSD/GPL
depends:
intree: Y
name: zram
retpoline: Y
vermagic: 7.2.3 SMP preempt mod_unload
parm: num_devices:Number of pre-created zram devices (uint)

Offhand it looks to me like compressed tmpfs, which sounds like a really good idea for systems with limited physical ram. You have my interest piqued and I am formulating a plan to test it soon. Normally I avoid compression but in this case it looks to be a desirable alternative to tmpfs. We'll see. Thanks for the heads up.

Het leven is goed,
Maurice

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Hey andy5995!

<Esc>:read !/usr/sbin/zramctl --version
zramctl from util-linux 2.42.2

<Esc>:read !/usr/sbin/zramctl --help

Usage:
zramctl [options] <device>
zramctl -r <device> [...]
zramctl [options] -f | <device> -s <size>

Set up and control zram devices.

Options:
-a, --algorithm <alg> compression algorithm to use
-b, --bytes print sizes in bytes, not in human-readable form
-f, --find find a free device
-n, --noheadings don't print headings
-o, --output <list> columns to use for status output
--output-all output all columns
-p, --algorithm-params <parameter>...
parameters for the compression algorithm
-r, --reset <device>... reset the specified zram devices
--raw use raw status output format
-s, --size <size> device size
-t, --streams <number> number of compression streams

-h, --help display this help
-V, --version display version

Arguments:
Values for <size> may be followed by a suffix: KiB, MiB,
GiB, TiB, PiB, EiB, ZiB, or YiB (where the "iB" is optional).
<alg> is the name of an algorithm; supported are:
lzo, lz4, lz4hc, deflate, 842, zstd
(List may be inaccurate, consult man page.)

Available output columns:
NAME zram device name
DISKSIZE limit on the uncompressed amount of data
DATA uncompressed size of stored data
COMPR compressed size of stored data
ALGORITHM the selected compression algorithm
STREAMS number of concurrent compress operations
ZERO-PAGES empty pages with no allocated memory
TOTAL all memory including allocator fragmentation and metadata overhead
MEM-LIMIT memory limit used to store compressed data
MEM-USED peak memory usage to store compressed data
MIGRATED number of objects migrated by compaction
COMP-RATIO compression ratio: DATA/TOTAL
MOUNTPOINT where the device is mounted

For more details see zramctl(8).

Life is good,
Maurice

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