MR proposed: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/262

MR for CKI for ARK proposed: https://gitlab.com/cki-project/kernel-ark/-/merge_requests/1528

a suggested action plan for testing: use zram disk with zstd compression

docs: https://www.kernel.org/doc/html/latest/admin-guide/blockdev/zram.html

### create one zram device
# modprobe zram num_devices=1

### check and set zstd compression 
# cat /sys/block/zram0/comp_algorithm 
lzo [lzo-rle] lz4 lz4hc 842 zstd 
# echo zstd > /sys/block/zram0/comp_algorithm
# cat /sys/block/zram0/comp_algorithm 
lzo lzo-rle lz4 lz4hc 842 [zstd] 
< *** the output must contain "[zstd]" here *** >

### set max ram usage = 256 Mbytes
# echo 256M > /sys/block/zram0/disksize

### write, read and test some data (/boot, for example)
# mke2fs -m 0 -b 4096 -O sparse_super -L zram /dev/zram0
# mount -o relatime,noexec,nosuid /dev/zram0 /mnt/zram
# cp -rp /boot /mnt/zram
# diff -rp /boot /mnt/zram/boot
< *** must be no output here *** >

### get funny stats
# awk '{ print "uncompressed size of data",$1,"\ncompressed size of data", $2, "\nmemory allocated for this disk", $3, "\nnumber of incompressible pages", $8 }' /sys/block/zram0/mm_stat
uncompressed size of data 185937920 
compressed size of data 163488509 
memory allocated for this disk 164663296 
number of incompressible pages 36615

### uncreate
# umount /mnt/zram
# rmmod zram

Can someone unmark this as "redhat" private? I think that got set by accident...

(In reply to Vladis Dronov from comment #5)
> a suggested action plan for testing: use zram disk with zstd compression

hi, Changhui,

i need to make a change to the suggested testing plan in #c5. in the current
version we will be reading data from a page cache, not from zram disk, so
compare operation will always succeed.

can you please consider the following change in a testing script:

...
### write some data (/boot, for example), un-mount and drop caches
# mkdir -p /mnt/zram
# mke2fs -m 0 -b 4096 -O sparse_super -L zram /dev/zram0
# mount -o relatime,noexec,nosuid /dev/zram0 /mnt/zram
# cp -rp /boot /mnt/zram
# umount /mnt/zram
# echo 3 > /proc/sys/vm/drop_caches

### test the data
# mount -o relatime,noexec,nosuid /dev/zram0 /mnt/zram
# diff -rp /boot /mnt/zram/boot
< *** must be no output here *** >

### clean up
# umount /mnt/zram
# rmdir /mnt/zram
# rmmod zram

Tested on 5.14.0-39.mrs_262_292.el9 with good results, 
zstd compression functionality has enabled, zstd smoke and zstd compression test passed.

# grep CONFIG_CRYPTO_ZSTD /boot/config-5.14.0-39.mrs_262_292.el9.x86_64
CONFIG_CRYPTO_ZSTD=m

# grep CONFIG_ZSTD_COMPRESS /boot/config-5.14.0-39.mrs_262_292.el9.x86_64
CONFIG_ZSTD_COMPRESS=m

:: [ 04:27:09 ] :: [  BEGIN   ] :: Running 'uname -a'
Linux storageqe-70.rhts.eng.pek2.redhat.com 5.14.0-39.mrs_262_292.el9.x86_64 #1 SMP PREEMPT Fri Jan 14 07:51:34 EST 2022 x86_64 x86_64 x86_64 GNU/Linux

::[04:27:09]::[BEGIN]:: Running 'cat /sys/block/zram0/comp_algorithm'
lzo lzo-rle [zstd]


::[04:27:11]::[BEGIN]:: Running 'diff -rp /boot /mnt/zram/boot'
:: [ 04:27:12 ] :: [ PASS ] :: Command 'diff -rp /boot /mnt/zram/boot' (Expected 0, got 0)


uncompressed size of data 261521408
compressed size of data 233442811
memory allocated for this disk 234971136
number of incompressible pages 52081

Tested on kernel-5.14.0-47.el9,
zstd compression functionality has enabled, zstd smoke and zstd compression test passed
https://beaker.engineering.redhat.com/jobs/6216984

# grep CONFIG_CRYPTO_ZSTD /boot/config-5.14.0-47.el9.x86_64 
CONFIG_CRYPTO_ZSTD=m
# grep CONFIG_ZSTD_COMPRESS /boot/config-5.14.0-47.el9.x86_64 
CONFIG_ZSTD_COMPRESS=m

move to verified

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (new packages: kernel), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2022:3907