[PROBLEM] RAM disk/drive on Xbian, how to use zramswap?

[postcd]

Hello,

one Kodi plugin downloads repeatedly a file worth tens of MB data and to save SDHC card writing cycles, I have found using "df -Th", that only tmpfs (RAM based filesystem per my understanding) is /dev and /run
# df -Th|grep tmpfs

Code:

devtmpfs       devtmpfs  1.6G   71M  1.5G   5% /dev
none           tmpfs     360M  748K  359M   1% /run
none           tmpfs     4.0K     0  4.0K   0% /sys/fs/cgroup

I may utilize /dev/bigfile.name if i "chown xbian /dev", but since it may not be good practice, but /run seems to have already writing permissions for all users "Access: (1777/drwxrwxrwt)". Beside that I was able to do:

Code:

mkdir -p /mnt/tmpfs
echo "tmpfs /mnt/tmpfs tmpfs size=100M,mode=0755,uid=xbian 0 0" >> /etc/fstab
mount -a

(allowing me to utilize /mnt/tmpfs/ directory as a RAM disk storage)

Yet someone suggested me to use zram with lz4 compression (claiming to be better compression than Xbian default lzo-rle) to save the space. Though i have doubts about this approach since zram is slower than regular tmpfs and if tmps/memory pressure is high, it will then move to zram swap per my understanding). But anyway if i want to do it, i tried these steps (failed):

# zramctl --output-all

Code:

NAME       DISKSIZE DATA COMPR ALGORITHM STREAMS ZERO-PAGES TOTAL MEM-LIMIT MEM-USED MIGRATED MOUNTPOINT
/dev/zram0     128M   4K   73B lzo-rle         4          0    4K        0B       4K       0B [SWAP]

# mount -t ext4 /dev/zram0 /mnt/zram

Code:

mount: /mnt/zram: /dev/zram0 already mounted or mount point busy.

# mount -t tmpfs /dev/zram0 /mnt/zram
# df -h

Code:

/dev/zram0      1.8G     0  1.8G   0% /mnt/zram
tmpfs           100M   26M   75M  26% /mnt/tmpfs

I am able to mount it automatically using /etc/fstab line:

Code:

/dev/zram0 /mnt/zram tmpfs size=100M,mode=0755,uid=xbian 0 0

I could do:
# swapoff -a;zramctl --algorithm lz4 --streams 4 --size 128M /dev/zram0 && swapon
# zramctl --output-all

Code:

NAME       DISKSIZE DATA COMPR ALGORITHM STREAMS ZERO-PAGES TOTAL MEM-LIMIT MEM-USED MIGRATED MOUNTPOINT
/dev/zram0     128M   0B    0B lz4             4          0    0B        0B       0B       0B

# free -h

Code:

Swap:             0B          0B          0B

I could write file to /mnt/zram/ but i see no zram usage:

# df -h /mnt/zram /mnt/tmpfs

Code:

Filesystem      Size  Used Avail Use% Mounted on
/dev/zram0      100M   26M   75M  26% /mnt/zram
tmpfs           100M   26M   75M  26% /mnt/tmpfs

# zramctl

Code:

NAME       ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 lz4           128M   0B    0B    0B       4

# free -h

Code:

total        used        free      shared  buff/cache   available
Mem:           3.5Gi       330Mi       2.4Gi       160Mi       808Mi       2.8Gi
Swap:             0B          0B          0B

and test the speed:

ioping -R /mnt/zram
-R, -rapid test with rapid I/O during 3s (-q -i 0 -w 3)

Code:

--- /mnt/zram (tmpfs /dev/zram0 100 MiB) ioping statistics ---
311.8 k requests completed in 2.45 s, 1.19 GiB read, 127.1 k iops, 496.6 MiB/s
generated 311.8 k requests in 3.00 s, 1.19 GiB, 103.9 k iops, 405.9 MiB/s
min/avg/max/mdev = 6.41 us / 7.87 us / 1.78 ms / 6.88 us

vs regular tmpfs:

Code:

--- /mnt/tmpfs (tmpfs tmpfs 100 MiB) ioping statistics ---
314.2 k requests completed in 2.46 s, 1.20 GiB read, 127.9 k iops, 499.6 MiB/s
generated 314.2 k requests in 3.00 s, 1.20 GiB, 104.7 k iops, 409.2 MiB/s
min/avg/max/mdev = 6.39 us / 7.82 us / 1.36 ms / 4.46 us

# fdisk -x /dev/zram0

Code:

Disk /dev/zram0: 128 MiB, 134217728 bytes, 32768 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

# lsblk -a

Code:

NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
ram0          1:0    0    4M  0 disk
ram1          1:1    0    4M  0 disk
...
zram0       254:0    0  128M  0 disk /mnt/zram
zram1       254:1    0    0B  0 disk
zram2       254:2    0    0B  0 disk
zram3       254:3    0    0B  0 disk

Do you have idea on /etc/fstab line to mount zram based filesystem please?

[Nachteule]

Simple answer:

xbian-package-zram-swap

/etc/default/zram-swap

[postcd]

> xbian-package-zram-swap

did "apt install xbian-package-zram-swap" -> "xbian-package-zram-swap is already the newest version (1.0.8)."

> /etc/default/zram-swap

is a config. file apparently, thanks. Being unsure how to modify it, i assumed i need to somehow activate zram so i did:

Quote:ZRUNSHM=1

After reboot, it caused following in "zramctl --output-all" output:

Quote:/dev/zram2 1M 44K 743B lzo-rle 4 1 24K 0B 24K 0B /run/shm

(only 1MB? Copying file to it says: No space left on device)

Quote:# grep -v "#" /etc/default/zram-swap|grep .
SIZE=128
SWAPFILE=
ZRUNSHM=1
ZTEMPXBMC=0
SWAPNOUSE='/dev/sda21,/dev/mmcblk0p99'

and mount:

Quote:/dev/zram2 on /run/shm type ext2 (rw,nosuid,noatime)

Quote:# swapon
NAME TYPE SIZE USED PRIO
/dev/zram0 partition 128M 0B 20
/dev/mmcblk0p3 partition 245M 0B 0

Setting SWAPFILE=/mnt/zram
not apparently changed outputs of above commands (file existed before reboot, after reboot not exist)

I wanted to have proper zram 128M partition and proper grow-able zramswap... any idea what to try please?

[Nachteule]

Moving shm to zram is complete nonsense in my opinion

Ever googled for zswap?

Since you obviously want to do everything yourself I can't help you there. and - please don't be angry - I don't have much desire to do that anymore either

[ontosalsa]

I learned about zswap on Google. I'm still having problems, but thanks for your feedback anyway.

[sortrequire]

(12th Jun, 2023 08:11 PM)Nachteule Wrote:  Moving shm to zram is complete nonsense in my opinion

Ever googled for zswap?

Since you obviously want to do everything yourself I can't help you there. and - please don't be angry - I don't have much desire to do that anymore either

I find it necessary to search for the right keywords to extract data. I'm doing research based on your suggestion. Looking forward to finding a solution.

[ngoutlandish]

This sounds like something from a Linux or performance optimization discussion, maybe about memory management? Are you troubleshooting something specific, or just sharing a frustrating exchange?

[annawhite]

Have you considered using zramfs instead of zram0 to mount directly as a filesystem? And have you tried writing large files to /mnt/zram to see when ZRAM actually compresses and takes up RAM? Because according to the parameters you shared, ZRAM is not "forced to work" due to the large amount of free memory.
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